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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Feb. 28, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	Celldex Therapeutics, Inc.
Entity Central Index Key	0000744218
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 313
Entity Common Stock, Shares Outstanding		141,073,668
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Assets:
Cash and Cash Equivalents	$ 40,288	$ 42,461
Marketable Securities	99,139	147,315
Accounts and Other Receivables	1,880	1,784
Prepaid and Other Current Assets	3,449	4,009
Total Current Assets	144,756	195,569
Property and Equipment, Net	10,372	13,192
Intangible Assets, Net	67,591	81,487
Other Assets	1,929	2,134
Goodwill	90,976	90,976
Total Assets	315,624	383,358
Current Liabilities:
Accounts Payable	1,715	1,740
Accrued Expenses	19,455	28,657
Current Portion of Long-Term Liabilities	6,566	4,826
Total Current Liabilities	27,736	35,223
Other Long-Term Liabilities	51,519	82,704
Total Liabilities	79,255	117,927
Commitments and Contingent Liabilities (Notes 13 and 15)
Stockholders' Equity:
Convertible Preferred Stock, $.01 Par Value; 3,000,000 Shares Authorized; No Shares Issued and Outstanding at December 31, 2017 and 2016
Common Stock, $.001 Par Value; 297,000,000 Shares Authorized; 138,520,404 and 120,516,654 Shares Issued and Outstanding at December 31, 2017 and 2016, respectively	139	121
Additional Paid-In Capital	1,046,183	982,255
Accumulated Other Comprehensive Income	2,564	2,541
Accumulated Deficit	(812,517)	(719,486)
Total Stockholders' Equity	236,369	265,431
Total Liabilities and Stockholders' Equity	$ 315,624	$ 383,358

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
CONSOLIDATED BALANCE SHEETS
Convertible Preferred Stock, Par Value (in dollars per share)	$ 0.01	$ 0.01
Convertible Preferred Stock, Shares Authorized	3,000,000	3,000,000
Convertible Preferred Stock, Shares Issued	0	0
Convertible Preferred Stock, Shares Outstanding	0	0
Common Stock, Par Value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, Shares Authorized	297,000,000	297,000,000
Common Stock, Shares Issued	138,520,404	120,516,654
Common Stock, Shares Outstanding	138,520,404	120,516,654

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
REVENUES:
Product Development and Licensing Agreements	$ 3,153	$ 2,174	$ 1,442
Contracts and Grants	9,590	4,612	4,038
Total Revenues	12,743	6,786	5,480
OPERATING EXPENSES:
Research and Development	96,171	102,726	100,171
General and Administrative	25,003	35,979	33,837
In-Process Research and Development Impairment	13,000
Gain on Fair Value Remeasurement of Contingent Consideration	(800)
Amortization of Acquired Intangible Assets	896	997	1,013
Total Operating Expenses	134,270	139,702	135,021
Operating Loss	(121,527)	(132,916)	(129,541)
Investment and Other Income, Net	4,214	4,386	2,344
Net Loss Before Income Tax Benefit	(117,313)	(128,530)	(127,197)
Income Tax Benefit	24,282
Net Loss	$ (93,031)	$ (128,530)	$ (127,197)
Basic and Diluted Net Loss Per Common Share (in dollars per share)	$ (0.72)	$ (1.27)	$ (1.31)
Shares Used in Calculating Basic and Diluted Net Loss per Share (in shares)	128,543	101,529	97,051
COMPREHENSIVE LOSS:
Net Loss	$ (93,031)	$ (128,530)	$ (127,197)
Other Comprehensive Income (Loss):
Foreign Currency Translation Adjustments			15
Unrealized Gain (Loss) on Marketable Securities	23	234	(298)
Comprehensive Loss	$ (93,008)	$ (128,296)	$ (127,480)

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Period Start Balance at Dec. 31, 2014	$ 90	$ 672,739	$ 2,590	$ (463,759)	$ 211,660
Balance (in shares) at Dec. 31, 2014	89,592,779
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans	$ 1	4,310			4,311
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	755,316
Shares Issued in Underwritten Offering	$ 8	188,832			188,840
Shares Issued in Underwritten Offering (in shares)	8,337,500
Share-Based Compensation		12,774			12,774
Foreign Currency Translation Adjustments			15		15
Unrealized Gains (Losses) on Marketable Securities			(298)		(298)
Net Loss				(127,197)	(127,197)
Period End Balance at Dec. 31, 2015	$ 99	878,655	2,307	(590,956)	290,105
Balance (in shares) at Dec. 31, 2015	98,685,595
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans	$ 1	534			535
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	158,152
Shares Issued in Connection with Cantor Agreement	$ 3	13,943			13,946
Shares Issued in Connection with Cantor Agreement (in shares)	3,303,800
Shares Issued in Connection with the Kolltan Acquisition	$ 18	73,379			73,397
Shares Issued in Connection with the Kolltan Acquisition (in shares)	18,257,996
Shares Issued in Connection with Kolltan Severance		427			427
Shares Issued in Connection with Kolltan Severance (in shares)	111,111
Share-Based Compensation		15,317			15,317
Unrealized Gains (Losses) on Marketable Securities			234		234
Net Loss				(128,530)	(128,530)
Period End Balance at Dec. 31, 2016	$ 121	982,255	2,541	(719,486)	$ 265,431
Balance (in shares) at Dec. 31, 2016	120,516,654				120,516,654
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans		265			$ 265
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	173,712
Shares Issued in Connection with Cantor Agreement	$ 18	51,007			51,025
Shares Issued in Connection with Cantor Agreement (in shares)	17,722,863
Shares Issued in Connection with Kolltan Severance		344			344
Shares Issued in Connection with Kolltan Severance (in shares)	107,175
Share-Based Compensation		12,312			12,312
Unrealized Gains (Losses) on Marketable Securities			23		23
Net Loss				(93,031)	(93,031)
Period End Balance at Dec. 31, 2017	$ 139	$ 1,046,183	$ 2,564	$ (812,517)	$ 236,369
Balance (in shares) at Dec. 31, 2017	138,520,404				138,520,404

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows From Operating Activities:
Net Loss	$ (93,031)	$ (128,530)	$ (127,197)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	4,414	3,095	2,998
Amortization of Intangible Assets	896	997	1,013
Amortization and Premium of Marketable Securities, Net	(290)	926	350
Loss on Sale or Disposal of Assets	55	81
In-Process Research and Development Impairment	13,000
Gain on Fair Value Remeasurement of Contingent Consideration	(800)
Non-Cash Income Tax Benefit	(24,282)
Stock-Based Compensation Expense	12,312	15,317	12,774
Non-Cash Expense		1,638	288
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	(96)	(814)	(543)
Prepaid and Other Current Assets	793	1,320	(653)
Other Assets	205	(89)	6
Accounts Payable and Accrued Expenses	(8,744)	(4,970)	4,875
Other Liabilities	(4,363)	(2,007)	7,202
Net Cash Used in Operating Activities	(99,931)	(113,036)	(98,887)
Cash Flows From Investing Activities:
Sales and Maturities of Marketable Securities	219,236	242,792	161,090
Purchases of Marketable Securities	(170,980)	(173,925)	(206,405)
Investment in Other		(1,801)
Cash Acquired in Kolltan Acquisition, Net		4,592
Acquisition of Property and Equipment	(1,788)	(2,751)	(4,876)
Net Cash Provided by (Used in) Investing Activities	46,468	68,907	(50,191)
Cash Flows From Financing Activities:
Net Proceeds from Stock Issuances	51,025	13,946	188,840
Proceeds from Issuance of Stock from Employee Benefit Plans	265	536	4,311
Net Cash Provided by Financing Activities	51,290	14,482	193,151
Effect of Exchange Rate Changes on Cash and Cash Equivalents			15
Net (Decrease) Increase in Cash and Cash Equivalents	(2,173)	(29,647)	44,088
Cash and Cash Equivalents at Beginning of Period	42,461	72,108	28,020
Cash and Cash Equivalents at End of Period	40,288	42,461	72,108
Non-cash Investing Activities
Accrued construction in progress	20	159	$ 75
Non-cash Supplemental Disclosure
Shares issued to former Kolltan executive for settlement of severance	$ 344	426
Shares issued in connection with Kolltan Acquisition		$ 73,397

Nature of Business and Overview	12 Months Ended
Nature of Business and Overview	Dec. 31, 2017
Nature of Business and Overview
Nature of Business and Overview	(1) Nature of Business and Overview Celldex Therapeutics, Inc. (the "Company" or "Celldex") is a biopharmaceutical company focused on the development and commercialization of several immunotherapy technologies and other cancer-targeting biologics. The Company currently has seven drug candidates in clinical development, including glembatumumab vedotin (also referred to as CDX-011), varlilumab (also referred to as CDX-1127), CDX-3379, CDX-014, CDX-1140, CDX-301 and CDX-1401. At December 31, 2017, the Company had cash, cash equivalents and marketable securities of $139.4 million. The Company has had recurring losses and incurred a loss of $93.0 million for the year ended December 31, 2017. Net cash used in operations for the year ended December 31, 2017 was $99.9 million. The Company believes that the cash, cash equivalents and marketable securities at March 7, 2018 will be sufficient to meet estimated working capital requirements and fund planned operations for at least the next twelve months from the date of issuance of these financial statements. During the next twelve months and beyond, the Company will take further steps to raise additional capital to meet its liquidity needs. These capital raising activities may include, but may not be limited to, one or more of the following: the licensing of drug candidates with existing or new collaborative partners, possible business combinations, issuance of debt, or the issuance of common stock or other securities via private placements or public offerings. While the Company may seek capital through a number of means, there can be no assurance that additional financing will be available on acceptable terms, if at all, and the Company's negotiating position in capital-raising efforts may worsen as existing resources are used. There is also no assurance that the Company will be able to enter into further collaborative relationships. Additional equity financings may be dilutive to the Company's stockholders; debt financing, if available, may involve significant cash payment obligations and covenants that restrict the Company's ability to operate as a business; and licensing or strategic collaborations may result in royalties or other terms which reduce the Company's economic potential from products under development. The Company's ability to continue funding its planned operations into and beyond twelve months from the issuance date is also dependent on the timing and manner of payment of future contingent milestones from the Kolltan acquisition, in the event that the Company achieves the drug candidate milestones related to those payments. The Company, at its option, may decide to pay those milestone payments in cash, shares of its common stock or a combination thereof. If the Company is unable to raise the funds necessary to meet its liquidity needs, it may have to delay or discontinue the development of one or more programs, discontinue or delay ongoing or anticipated clinical trials, license out programs earlier than expected, raise funds at a significant discount or on other unfavorable terms, if at all, or sell all or a part of the Company.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

(2) Summary of Significant Accounting Policies

Basis of Presentation

The balance sheets and statements of operations and comprehensive loss, stockholders' equity, and cash flows, are consolidated for the years ended December 31, 2017 and 2016. In February 2016, the Company formed a wholly-owned subsidiary, Celldex Therapeutics Europe GmbH, in Zug, Switzerland, which was liquidated in June 2017. In July 2016, the Company formed a wholly-owned subsidiary, Celldex Australia Pty Ltd, in Brisbane, Australia. These consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company operates in one segment, which is the business of development, manufacturing and commercialization of novel therapeutics for human health care.

Use of Estimates

The preparation of the financial statements in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP) requires management to make estimates and use assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the dates of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with a maturity date of 90 days or less at the date of purchase to be cash equivalents. Cash equivalents consist principally of money market funds and debt securities.

Marketable Securities

The Company invests its excess cash balances in marketable securities, including municipal bond securities, U.S. government agency securities, and highly rated corporate bonds. The Company classifies all of its marketable securities as current assets on the balance sheets because they are available-for-sale and available to fund current operations. Marketable securities are stated at fair value with unrealized gains and losses included as a component of accumulated other comprehensive income (loss), which is a separate component of stockholders' equity, until such gains and losses are realized. If a decline in the fair value is considered other-than-temporary, based on available evidence, the unrealized loss is reclassified from accumulated other comprehensive income (loss) to the statements of operations. Realized gains and losses are determined on the specific identification method and are included in investment and other income, net.

Concentration of Credit Risk and of Significant Customers and Suppliers

Financial instruments that potentially subject the Company to concentrations of credit risk primarily consist of cash, cash equivalents, marketable securities and accounts receivable. The Company invests its cash, cash equivalents and marketable securities in debt instruments and interest-bearing accounts at major financial institutions in excess of insured limits. The Company mitigates credit risk by limiting the investment type and maturity to securities that preserve capital, maintain liquidity and have a high credit quality. The Company has not historically experienced credit losses from its accounts receivable and therefore has not established an allowance for doubtful accounts.

Combined revenue from International AIDS Vaccine Initiative, Frontier Biotechnologies, Inc. and BMS represented 73% of total Company revenue for the year ended December 31, 2017. Combined revenue from Rockefeller and BMS represented 71% and 86% of total Company revenue for the years ended December 31, 2016 and 2015, respectively.

The Company relies on contract manufacturing organizations (CMO) to manufacture drug substance and drug product for its late-stage clinical study of glembatumumab vedotin as well as for future commercial supplies. The Company also relies on CMOs for supply of raw materials as well as filling, packaging, storage and shipping of drug product. These clinical studies would be adversely affected by a significant interruption in the supply of glembatumumab vedotin. The Company also relies on third-party collaborators to develop companion diagnostic tests for certain of its drug candidates, including glembatumumab vedotin.

Fair Value Measurements

The Company has certain assets and liabilities that are measured at fair value in the financial statements. The Company seeks to maximize the use of observable inputs (market data obtained from sources independent from the Company) and to minimize the use of unobservable inputs (the Company's assumptions about how market participants would price assets and liabilities) when measuring the fair value of its assets and liabilities. These assets and liabilities are classified into one of three levels of the following fair value hierarchy as defined by U.S. GAAP:

Level 1: Observable inputs such as quoted prices in active markets for identical assets or liabilities. An active market for an asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis.

Level 2: Observable inputs other than Level 1 prices, such as quoted prices in active markets for similar assets or liabilities and quoted prices for identical assets or liabilities in markets that are not active.

Level 3: Unobservable inputs based on the Company's assessment of the assumptions that market participants would use in pricing the asset or liability.

Property and Equipment

Property and equipment is stated at cost and depreciated over the estimated useful lives of the related assets using the straight-line method. Laboratory equipment and office furniture and equipment are depreciated over five years, and computer equipment is depreciated over three years. Manufacturing equipment is amortized over seven to ten years. Leasehold improvements are amortized over the shorter of the estimated useful life or the non-cancelable term of the related lease, including any renewals that are reasonably assured of occurring. Property and equipment under construction is classified as construction in progress and is depreciated or amortized only after the asset is placed in service. Expenditures for maintenance and repairs are charged to expense whereas the costs of significant improvements which extend the life of the underlying asset are capitalized. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are eliminated and any resulting gain or loss is reflected in the Company's statements of operations and comprehensive loss.

The treatment of costs to construct property and equipment depends on the nature of the costs and the stage of construction. Costs incurred in the project planning, design, construction and installation phases are capitalized as part of the cost of the asset. The Company stops capitalizing these costs when the asset is substantially complete and ready for its intended use. For manufacturing property and equipment, the Company also capitalizes the cost of validating these assets for the underlying manufacturing process. The Company completes the capitalization of validation costs when the asset is substantially complete and ready for its intended use. Costs capitalized include incremental labor and fringe benefits, and direct consultancy services.

Other Assets

Other assets include a $1.8 million non-controlling investment in a privately-held company that is accounted for under the cost method of accounting as of December 31, 2017 and 2016. The Company periodically evaluates the carrying value of the investment if significant adverse events or circumstances indicate an impairment in value.

Business Combinations

The Company records the fair value of the consideration transferred to acquire a business to the tangible assets and identifiable intangible assets acquired and liabilities assumed on the basis of their fair values at the date of acquisition. The Company assesses the fair value of assets, including intangible assets such as in-process research and development (IPR&D), using a variety of methods including present-value models. Each asset is measured at fair value from the perspective of a market participant. The method used to estimate the fair values of IPR&D assets incorporates significant assumptions regarding the estimates a market participant would make in order to evaluate an asset, including a market participant's assumptions regarding the probability of completing IPR&D projects, which would require obtaining regulatory approval for marketing of the associated drug candidate; a market participant's estimates regarding the timing of and the expected costs to complete IPR&D projects; a market participant's estimates of future cash flows from potential product sales; and the appropriate discount rates for a market participant. Transaction costs and restructuring costs associated with the transaction are expensed as incurred.

The Company records contingent consideration resulting from a business combination at its fair value on the acquisition date. The Company determines the fair value of the contingent consideration based primarily on the (i) timing and probability of success of clinical events or regulatory approvals; (ii) timing and probability of success of meeting clinical and commercial milestones; and (iii) discount rates. The Company's contingent consideration liabilities arose in connection with its acquisition of Kolltan. On a quarterly basis, the Company revalues these obligations and records increases or decreases in their fair value as an adjustment to operating earnings. Changes to contingent consideration obligations can result from adjustments to discount rates, accretion of the discount rates due to the passage of time, changes in the Company's estimates of the likelihood or timing of achieving development or commercial milestones, changes in the probability of certain clinical events or changes in the assumed probability associated with regulatory approval. The assumptions related to determining the value of contingent consideration include a significant amount of judgment, and any changes in the underlying estimates could have a material impact on the amount of contingent consideration expense recorded in any given period.

Intangible Assets

IPR&D assets acquired in a business combination initially are recorded at fair value and accounted for as indefinite-lived intangible assets. These assets are capitalized on the Company's balance sheets until either the project underlying them is completed or the assets become impaired. If a project is completed, the carrying value of the related intangible asset is amortized over the remaining estimated life of the asset beginning in the period in which the project is completed. If a project becomes impaired or is abandoned, the carrying value of the related intangible asset is written down to its fair value and an impairment charge is taken in the period in which the impairment occurs.

Each IPR&D asset is assessed for impairment at least annually or when impairment indicators are present. During the year ended December 31, 2017, we recorded a partial impairment charge of $13.0 million related to changes in projected development and regulatory timelines regarding the anti-KIT program. The remaining IPR&D assets were assessed for impairment during 2017 and were determined not to be impaired.

Intangible assets acquired in a business combination with a finite life are recorded at fair value and amortized over the greater of economic consumption or on a straight-line basis over their estimated useful life.

Goodwill

The difference between the purchase price and the fair value of assets acquired and liabilities assumed in a business combination is allocated to goodwill. Goodwill is evaluated for impairment on an annual basis during the third quarter, or earlier if impairment indicators are present. The Company has the option to assess qualitative factors to determine if it is more likely than not that goodwill might be impaired and whether it is necessary to perform a quantitative single-step goodwill impairment test required under U.S. GAAP. As part of its annual impairment test of the goodwill asset as of July 1, 2017, the Company bypassed the optional qualitative assessment and performed a quantitative assessment under the single-step impairment assessment. The Company concluded that goodwill was not impaired.

Impairment of Intangible and Long-Lived Assets

The Company evaluates the recoverability of its long-lived assets, including property and equipment, and intangible assets when circumstances indicate that an event of impairment may have occurred. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the asset and its eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their estimated fair values.

Revenue Recognition

The Company recognizes revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; delivery has occurred or services have been rendered; the seller's price to the buyer is fixed or determinable; and collectability is reasonably assured.

The Company has entered into and in the future may enter into biopharmaceutical product development agreements with collaborative partners for the research and development of therapeutic drug candidates. The terms of the agreements may include nonrefundable signing and licensing fees, funding for research, development and manufacturing, milestone payments and royalties on any product sales derived from collaborations. These multiple element arrangements are analyzed to determine whether the deliverables can be separated or whether they must be accounted for as a single unit of accounting. In accounting for these transactions, the Company allocates revenue to the various elements based on their relative fair value. The fair value of a revenue generating element can be based on current selling prices offered by the Company or another party for current products or the Company's best estimate of a selling price for future products. Revenue allocated to an individual element is recognized when all other revenue recognition criteria are met for that element.

These collaborative and other agreements may contain milestone payments. Revenues from milestones, if they are considered substantive, are recognized upon successful accomplishment of the milestones. Determining whether a milestone is substantive involves judgment, including an assessment of the Company's involvement in achieving the milestone and whether the amount of the payment is commensurate to the Company's performance. If not considered substantive, milestones are initially deferred and recognized over the period of the remaining performance obligation.

Payments received to fund certain research activities are recognized as revenue in the period in which the research activities are performed. Revenue from contracts and grants is recognized as the services are performed and recorded as effort is expended on the contracted work and billed to the government or the Company's contractual partner. Payments received in advance that are related to future performance are deferred and recognized as revenue when the research projects are performed.

Product royalty revenue consists of payments received from licensees for a portion of sales proceeds from products that utilize the Company's licensed technologies and is recognized when the amount of and basis for such royalty payments are reported to the Company in accurate and appropriate form and in accordance with the related license agreement.

Research and Development Expenses

Research and development costs, including internal and contract research costs, are expensed as incurred. Research and development expenses consist mainly of clinical trial costs, manufacturing of clinical material, toxicology and other preclinical studies, personnel costs, depreciation, license fees and funding of outside contracted research.

Clinical trial expenses include expenses associated with clinical research organization, or CRO, services. Contract manufacturing expenses include expenses associated with contract manufacturing organization, or CMO, services. The invoicing from CROs and CMOs for services rendered can lag several months. The Company accrues the cost of services rendered in connection with CRO and CMO activities based on our estimate of costs incurred. The Company maintains regular communication with our CROs and CMOs to assess the reasonableness of its estimates. Differences between actual expenses and estimated expenses recorded have not been material and are adjusted for in the period in which they become known.

Patent Costs

Patent costs are expensed as incurred. Certain patent costs are reimbursed by the Company's product development and licensing partners. Any reimbursed patent costs are recorded as product development and licensing agreement revenues in the Company's financial statements.

Stock-Based Compensation

The Company records stock-based compensation expense for all stock-based awards made to employees and directors based on the estimated fair values of the stock-based awards expected to vest at the grant date and is adjusted, if necessary, to reflect actual forfeitures. Compensation expense for all stock-based awards to employees and directors is recognized using the straight-line method over the term of vesting or performance.

The Company records stock-based compensation expense for stock options granted to non-employees based on the fair value of the stock options which is re-measured over the graded vesting term resulting in periodic adjustments to stock-based compensation expense.

Foreign Currency Translation

Net unrealized gains and losses resulting from foreign currency translation are included in accumulated other comprehensive income. At December 31, 2017 and 2016, accumulated other comprehensive income includes a net unrealized gain related to foreign currency translation of $2.6 million.

Income Taxes

The Company uses the asset and liability method to account for income taxes, including the recognition of deferred tax assets and deferred tax liabilities for the anticipated future tax consequences attributable to differences between financial statement amounts and their respective tax basis. Quarterly, the Company reviews its deferred tax assets for recovery. A valuation allowance is established when the Company believes that it is more likely than not that its deferred tax assets will not be realized. Changes in valuation allowances from period to period are included in the Company's tax provision in the period of change.

The Company records uncertain tax positions in the financial statements only if it is more likely than not that the uncertain tax position will be sustained upon examination by the taxing authorities. The Company records interest and penalties related to uncertain tax positions in income tax expense.

Comprehensive Loss

Comprehensive loss is comprised of net loss and certain changes in stockholders' equity that are excluded from net loss. The Company includes foreign currency translation adjustments and unrealized gains and losses on marketable securities in other comprehensive loss. The statements of operations and comprehensive loss reflect total comprehensive loss for the years ended December 31, 2017, 2016 and 2015.

Net Loss Per Share

Basic net loss per common share is based upon the weighted-average number of common shares outstanding during the period, excluding restricted stock that has been issued but is not yet vested. Diluted net loss per common share is based upon the weighted-average number of common shares outstanding during the period plus additional weighted-average potentially dilutive common shares outstanding during the period when the effect is dilutive. The potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive are as follows:

	Year Ended December 31,
	2017		2016		2015
Stock options		10,856,212		10,218,710		8,110,239
Restricted stock		96,668		50,000		19,500

		10,952,880		10,268,710		8,129,739

Newly-Adopted Accounting Pronouncements

On January 1, 2017, the Company adopted a new accounting standard which involves several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The Company elected to continue to estimate forfeitures expected to occur to determine stock-based compensation expense. Upon adoption, the Company's gross deferred tax assets and corresponding valuation allowance each increased by $17.7 million related to tax deductions from the exercise of stock options that previously would have been credited to additional paid-in-capital when realized.

On January 1, 2017, the Company adopted a new accounting standard which simplifies how an entity tests goodwill for impairment. A goodwill impairment is now calculated under a single-step quantitative test which compares a reporting unit's carrying value to its fair value. A goodwill impairment is the amount by which the carrying value of the reporting unit exceeds its fair value, not to exceed the carrying amount of goodwill. Under this standard, the Company continues to have the option to perform a qualitative assessment to determine if the single-step quantitative test is necessary.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board ("FASB") or other standard setting bodies that are adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on the Company's consolidated financial statements upon adoption.

In May 2014, the FASB issued a new accounting standard that updates guidance and disclosure requirements for recognizing revenue. The new revenue recognition standard provides a five-step model for recognizing revenue from contracts with customers. The core principle is that a company should recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods and services.

The Company will adopt the new revenue standard as of January 1, 2018 using the modified retrospective application method. All material open contracts as of December 31, 2017 were identified by the Company and assessed under the updated revenue recognition guidance. As of December 31, 2017, the Company had finalized its assessment of the impact of this standard and expects to recognize an immaterial decrease to both accumulated deficit and deferred revenue on January 1, 2018. As a result of adopting this standard, the Company has implemented additional processes and controls, and plans to include additional disclosures in future filings to comply with this standard.

In February 2016, the FASB issued a new accounting standard which requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. The new standard will be effective for the Company on January 1, 2019. The Company is currently evaluating the potential impact that this standard may have on the Company's consolidated financial statements.

In August 2016, the FASB issued updated guidance which clarifies the classification of certain cash receipts and payments in the statement of cash flows. This standard is effective for the company on January 1, 2018. The adoption of this new guidance is not expected to have a material impact on the Company's consolidated financial statements.

Accumulated Other Comprehensive Income

12 Months Ended

Dec. 31, 2017

Accumulated Other Comprehensive Income

Accumulated Other Comprehensive Income

(3) Accumulated Other Comprehensive Income

The changes in accumulated other comprehensive income, which is reported as a component of stockholders' equity, for the year ended December 31, 2017 are summarized below:

	Unrealized Gain (Loss) on Marketable Securities			Foreign Currency Items		Total
	(In thousands)
Balance at December 31, 2016	$	(55	)	$	2,596	$	2,541
Other comprehensive gain		23			—		23

Balance at December 31, 2017	$	(32	)	$	2,596	$	2,564

No amounts were reclassified out of accumulated other comprehensive income during the years ended December 31, 2017, 2016 and 2015.

- Definition

The entire disclosure for comprehensive income, which includes, but is not limited to, 1) the amount of income tax expense or benefit allocated to each component of other comprehensive income, including reclassification adjustments, 2) the reclassification adjustments for each classification of other comprehensive income and 3) the ending accumulated balances for each component of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e689-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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-Section 45
-Paragraph 1A
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 220
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Reclassification Adjustments
-URI http://asc.fasb.org/extlink&oid=6522872

+ Details

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Measurements

Fair Value Measurements

(4) Fair Value Measurements

The following tables set forth the Company's financial assets and liabilities subject to fair value measurements:

	As of December 31, 2017		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	24,061		—	$	24,061		—
Marketable securities		99,139		—		99,139		—

	$	123,200		—	$	123,200		—


Liabilities:
Kolltan acquisition contingent consideration	$	43,400		—		—	$	43,400

	$	43,400		—		—	$	43,400

	As of December 31, 2016		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	20,445		—	$	20,445		—
Marketable securities		147,315		—		147,315		—

	$	167,760		—	$	167,760		—


Liabilities:
Kolltan acquisition contingent consideration	$	44,200		—		—	$	44,200

	$	44,200		—		—	$	44,200

The Company's financial assets consist mainly of cash and cash equivalents and marketable securities and are classified as Level 2 within the valuation hierarchy. The Company values its marketable securities utilizing independent pricing services which normally derive security prices from recently reported trades for identical or similar securities, making adjustments based on significant observable transactions. At each balance sheet date, observable market inputs may include trade information, broker or dealer quotes, bids, offers or a combination of these data sources.

The following table reflects the activity for the Company's contingent consideration liabilities measured at fair value using Level 3 inputs for the year ended December 31, 2017 (in thousands):

	Other Liabilities: Contingent Consideration
Balance at December 31, 2016	$	44,200
Fair value adjustments included in operating expenses		(800	)

Balance at December 31, 2017	$	43,400

The valuation technique used to measure fair value of the Company's Level 3 liabilities, which consist of contingent consideration related to the acquisition of Kolltan in 2016 (Note 17), was primarily an income approach. The Company may be required to pay future consideration of up to $172.5 million that is contingent upon the achievement of specified development, regulatory approvals or sales-based milestone events. The significant unobservable inputs used in the fair value measurement of the contingent consideration are estimates, including probability of success, discount rates and amount of time until the conditions of the milestone payments are met.

During the year ended December 31, 2017, the Company recorded a $0.8 million gain on fair value remeasurement of contingent consideration, primarily due to a reduction in fair value attributed to the milestones related to the Company's anti-KIT and TAM programs and partially offset by losses related to changes in discount rates, passage of time and probabilities affecting remaining milestones. The Company's anti-KIT program includes CDX-0158 and CDX-0159, a variant of CDX-0158. CDX-0159 is being fully developed in-house with the intention of replacing CDX-0158 in clinical development.

The Company did not have any transfers of assets or liabilities between the fair value measurement classifications during the years ended December 31, 2017 and 2016.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Marketable Securities

12 Months Ended

Dec. 31, 2017

Marketable Securities

Marketable Securities

(5) Marketable Securities

The following is a summary of marketable securities, classified as available-for-sale:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(In thousands)
December 31, 2017
Marketable securities
U.S. government and municipal obligations
Maturing in one year or less	$	26,164	$	3	$	(9	)	$	26,158
Maturing after one year through three years		—		—		—			—

Total U.S. government and municipal obligations	$	26,164	$	3	$	(9	)	$	26,158

Corporate debt securities
Maturing in one year or less	$	73,007	$	1	$	(27	)	$	72,981
Maturing after one year through three years		—		—		—			—

Total corporate debt securities	$	73,007	$	1	$	(27	)	$	72,981

Total marketable securities	$	99,171	$	4	$	(36	)	$	99,139


December 31, 2016
Marketable securities
U.S. government and municipal obligations
Maturing in one year or less	$	52,754	$	5	$	(12	)	$	52,747
Maturing after one year through three years		296		8		—			304

Total U.S. government and municipal obligations	$	53,050	$	13	$	(12	)	$	53,051

Corporate debt securities
Maturing in one year or less	$	94,320	$	—	$	(56	)	$	94,264
Maturing after one year through three years		—		—		—			—

Total corporate debt securities	$	94,320	$	—	$	(56	)	$	94,264

Total marketable securities	$	147,370	$	13	$	(68	)	$	147,315

The Company holds investment grade marketable securities, and none were considered to be other-than-temporarily impaired as of December 31, 2017. Marketable securities include $0.3 million and $0.6 million in accrued interest at December 31, 2017 and December 31, 2016, respectively.

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

Property and Equipment, Net

12 Months Ended

Dec. 31, 2017

Property and Equipment, Net

Property and Equipment, Net

(6) Property and Equipment, Net

Property and Equipment, Net includes the following:

	December 31, 2017			December 31, 2016
	(In thousands)
Laboratory Equipment	$	7,770		$	6,771
Manufacturing Equipment		4,354			4,312
Office Furniture and Equipment		3,764			3,677
Leasehold Improvements		17,164			17,115
Construction in Progress		932			1,283

Total Property and Equipment		33,984			33,158
Less: Accumulated Depreciation and Amortization		(23,612	)		(19,966	)

Property and Equipment, Net	$	10,372		$	13,192

Depreciation and amortization expense related to property and equipment was $4.4 million, $3.1 million and $3.0 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Intangible Assets and Goodwill

12 Months Ended

Dec. 31, 2017

Intangible Assets and Goodwill

Intangible Assets and Goodwill

(7) Intangible Assets and Goodwill

Intangible Assets, Net

The table below presents information for the Company's finite-lived intangible assets that are subject to amortization and indefinite-lived intangible assets:

		December 31, 2017							December 31, 2016
	Estimated Life	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
		(In thousands)
Finite-lived Intangible Assets:
License Rights	16 years	$	14,500	$	(7,399	)	$	7,101	$	14,500	$	(6,503	)	$	7,997

Indefinite-lived Intangible Assets:
IPR&D	Indefinite		60,490		—			60,490		73,490		—			73,490

Total Intangible Assets, Net		$	74,990	$	(7,399	)	$	67,591	$	87,990	$	(6,503	)	$	81,487

Indefinite-lived intangible assets consist of acquired in-process research and development ("IPR&D") related to the development of glembatumumab vedotin, CDX-3379, the anti-KIT program and the TAM program. As of December 31, 2017, no IPR&D asset had reached technological feasibility nor did any have alternative future uses.

The Company performs an impairment test on IPR&D assets at least annually, or more frequently if events or changes in circumstances indicate that IPR&D assets may be impaired. During the year ended December 31, 2017, the Company recorded a non-cash partial impairment charge of $13.0 million on the anti-KIT program IPR&D assets acquired from Kolltan. The Company determined that changes in projected development and regulatory timelines related to the anti-KIT program taken together constituted a triggering event that required the Company to evaluate the intangible asset for impairment. As part of this evaluation, the present value of probability adjusted estimated net future cash flows was used to determine the fair value of the program and compared to the carrying value of the program. As a result of this impairment assessment, the Company concluded that a non-cash partial impairment charge of $13.0 million on the anti-KIT program IPR&D asset be recorded for the year ended December 31, 2017 for the amount the fair value of the anti-KIT program exceeded its carrying amount.

Due to the nature of IPR&D projects, the Company may experience future delays or failures to obtain regulatory approvals to conduct clinical trials, failures of such clinical trials or other failures to achieve a commercially viable product, and as a result, may recognize further impairment losses in the future.

Amortization expense for intangible assets was $0.9 million for the year ended December 31, 2017 and $1.0 million for both the years ended December 31, 2016 and 2015. The future amortization expense of intangible assets is estimated to be $0.9 million for each of the years ending December 31, 2018, 2019, 2020, 2021 and 2022.

Goodwill

There have been no changes to the carrying amount of goodwill during the year ended December 31, 2017. The Company performs an annual impairment test of goodwill as of July 1 each year. The Company tested goodwill for impairment as of July 1, 2017 and concluded that goodwill was not impaired.

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

Accrued Expenses

12 Months Ended

Dec. 31, 2017

Accrued Expenses

Accrued Expenses

(8) Accrued Expenses

Accrued expenses include the following:

	December 31, 2017		December 31, 2016
	(In thousands)
Accrued Payroll and Employee Benefits	$	6,348	$	7,132
Accrued Research and Development Contract Costs		11,399		17,742
Accrued Professional Fees		1,408		1,146
Other Accrued Expenses		300		2,637

	$	19,455	$	28,657

Other Long-Term Liabilities

12 Months Ended

Dec. 31, 2017

Other Long-Term Liabilities

Other Long-Term Liabilities

(9) Other Long-Term Liabilities

Other long-term liabilities include the following:

	December 31, 2017			December 31, 2016
	(In thousands)
Net Deferred Tax Liabilities Related to IPR&D (Note 14)	$	3,772		$	28,054
Deferred Income From Sale of Tax Benefits		6,756			9,436
Other		1,344			2,091
Contingent Milestones (Note 4)		43,400			44,200
Deferred Revenue		2,813			3,749

Total		58,085			87,530
Less Current Portion		(6,566	)		(4,826	)

Long-Term Portion	$	51,519		$	82,704

In November 2015, December 2014, January 2014 and January 2013, the Company received approval from the New Jersey Economic Development Authority and agreed to sell New Jersey tax benefits of $9.8 million, $1.9 million, $1.1 million and $0.8 million to an independent third party for $9.2 million, $1.8 million, $1.0 million and $0.8 million, respectively. Under the agreement, the Company must maintain a base of operations in New Jersey for five years or the tax benefits must be paid back on a pro-rata basis based on the number of years completed. During the years ended December 31, 2017, 2016 and 2015, the Company recorded $2.7 million, $2.8 million and $1.0 million to other income related to the sale of these tax benefits, respectively.

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2017
Stockholders' Equity
Stockholders' Equity	(10) Stockholders' Equity Common Stock In December 2013, the Company filed an automatic shelf registration statement with the Securities and Exchange Commission to register for sale any combination of the types of securities described in the shelf registration statement. In December 2016, the Company filed a new shelf registration statement with the Securities and Exchange Commission to register for sale any combination of the types of securities described in the shelf registration statement up to a maximum aggregate offering price of $250 million. Such registration statement was declared effective on February 13, 2017. In May 2016, the Company entered into an agreement with Cantor Fitzgerald & Co. ("Cantor") to allow the Company to issue and sell shares of its common stock having an aggregate offering price of up to $60.0 million from time to time through Cantor, acting as agent. In November 2017, the Company filed a prospectus supplement registering the offer and sale of shares of common stock of up to an additional $75.0 million under the agreement with Cantor. During the years ended December 31, 2017 and 2016, the Company issued 17,722,863 and 3,303,800 shares of its common stock, respectively, under this controlled equity offering sales agreement with Cantor resulting in net proceeds to the Company of $51.0 million and $13.9 million, respectively, after deducting commission and offering expenses. At December 31, 2017, the Company had $67.6 million remaining in aggregate gross offering price available under the Cantor agreement. From January 1, 2018 through February 28, 2018, the Company issued 2,401,847 shares of its common stock resulting in net proceeds to the Company of $6.1 million. During the year ended December 31, 2015, the Company issued 8,337,500 shares of its common stock in underwritten public offerings resulting in net proceeds to the Company of $188.8 million after deducting underwriting fees and offering expenses. Convertible Preferred Stock At December 31, 2017, the Company had authorized 3,000,000 shares of preferred stock all of which have been designated Class C Preferred Stock including 350,000 shares which have been designated Series C-1 Junior Participating Cumulative Preferred Stock (the "Series C-1 Preferred Stock"). No shares of Series C-1 Preferred Stock were outstanding at December 31, 2017 or 2016.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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+ Details

Stock-Based Compensation

12 Months Ended

Dec. 31, 2017

Stock-Based Compensation

Stock-Based Compensation

(11) Stock-Based Compensation

The Company has the following stock-based compensation plans: the 2004 Employee Stock Purchase Plan (the "2004 ESPP Plan"), the 2008 Stock Option and Incentive Plan (the "2008 Plan") and Celldex Research's 2005 Equity Incentive Plan (the "Celldex Research 2005 Plan"). There are no shares available for future grant under the Celldex Research 2005 Plan.

Employee Stock Purchase Plan

At December 31, 2017, a total of 400,000 shares of common stock are reserved for issuance under the 2004 ESPP Plan. Under the 2004 ESPP Plan, each participating employee may purchase shares of common stock through payroll deductions at a purchase price equal to 85% of the lower of the fair market value of the common stock at either the beginning of the offering period or the applicable exercise date. During the years ended December 31, 2017, 2016 and 2015, the Company issued 80,379, 59,335 and 15,755 shares under the 2004 ESPP Plan, respectively. At December 31, 2017, 197,857 shares were available for issuance under the 2004 ESPP Plan.

Employee Stock Option and Incentive Plan

The 2008 Plan permits the granting of incentive stock options (intended to qualify as such under Section 422A of the Internal Revenue Code of 1986, as amended), non-qualified stock options, stock appreciation rights, performance share units, restricted stock and other awards of restricted stock in lieu of cash bonuses to employees, consultants and non-employee directors.

At December 31, 2017, the 2008 Plan allowed for a maximum of 20,000,000 shares of common stock to be issued for grants of new awards until June 9, 2025 and grants of incentive stock options until April 16, 2025. The Company's board of directors determines the term of each option, option price, and number of shares for which each option is granted and the rate at which each option vests. Options generally vest over a period not to exceed four years. The term of each option cannot exceed ten years (five years for options granted to holders of more than 10% of the voting stock of the Company), and the exercise price of stock options cannot be less than the fair market value of the common stock at the date of grant (110% of fair market value for incentive stock options granted to holders of more than 10% of the voting stock of the Company). Vesting of all employee and non-employee director stock option awards may accelerate upon a change in control as defined in the 2008 Plan.

A summary of stock option activity for the year ended December 31, 2017 is as follows:

	Shares			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at December 31, 2016		10,218,710		$	11.14		6.5
Granted		2,427,200		$	2.37
Exercised		—		$	—
Canceled		(1,789,698	)	$	9.76

Options Outstanding at December 31, 2017		10,856,212		$	9.40		6.1


Options Vested and Expected to Vest at December 31, 2017		10,780,023		$	9.43		6.1
Options Exercisable at December 31, 2017		6,846,254		$	11.18		4.5
Shares Available for Grant Under the 2008 Plan		8,324,310

The total intrinsic value of stock options exercised during the years ended December 31, 2017, 2016 and 2015 was $0.0 million, $0.1 million and $14.4 million, respectively. The weighted average grant-date fair value of stock options granted during the years ended December 31, 2017, 2016 and 2015 was $1.58, $3.18 and $15.25, respectively. The total fair value of stock options vested during the years ended December 31, 2017, 2016 and 2015 was $13.4 million, $17.0 million and $10.0 million, respectively.

The aggregate intrinsic value of stock options outstanding at December 31, 2017 was $1.1 million. The aggregate intrinsic value of stock options vested and expected to vest at December 31, 2017 was $1.1 million. As of December 31, 2017, total compensation cost related to non-vested employee and non-employee director stock options not yet recognized was approximately $15.0 million, net of estimated forfeitures, which is expected to be recognized as expense over a weighted average period of 2.7 years.

Restricted Stock

A summary of restricted stock activity under the 2008 Plan for the year ended December 31, 2017 is as follows:

	Shares			Weighted Average Grant Date Fair Value (per share)
Outstanding and unvested at December 31, 2016		50,000		$	4.72
Granted		70,000		$	2.32
Vested		(16,665	)	$	4.72
Canceled		(6,667	)	$	4.72

Outstanding and unvested at December 31, 2017		96,668		$	2.98

Valuation and Expenses Information

Stock-based compensation expense for the years ended December 31, 2017, 2016 and 2015 was recorded as follows:

	2017		2016		2015
	(In thousands)
Research and development	$	6,693	$	7,821	$	6,186
General and administrative		5,619		7,496		6,588

Total stock-based compensation expense	$	12,312	$	15,317	$	12,774

The fair values of employee and director stock options granted during the years ended December 31, 2017, 2016 and 2015 were valued using the Black-Scholes option pricing model with the following assumptions:

	2017	2016	2015
Expected stock price volatility	75 - 77%	70 - 77%	67 - 69%
Expected option term	6.0 Years	6.0 Years	6.0 Years
Risk-free interest rate	2.0 - 2.3%	1.4 - 2.3%	1.8 - 2.2%
Expected dividend yield	None	None	None

The Company estimates expected term based on historical exercise patterns. The Company uses its historical stock price volatility consistent with the expected term of grant as the basis for its expected volatility assumption. The risk-free interest rate is based upon the yield of U.S. Treasury securities consistent with the expected term of the option. The dividend yield assumption is based on the Company's history of zero dividend payouts and expectation that no dividends will be paid in the foreseeable future.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Revenue	12 Months Ended
Revenue	Dec. 31, 2017
Revenue
Revenue	(12) Revenue Rockefeller University (Rockefeller) In 2013, the Company entered into an agreement, as amended, with Rockefeller pursuant to which the Company performs research and development services for Rockefeller. The Company bills Rockefeller quarterly for actual time and direct costs incurred and records those amounts to revenue in the quarter the services are performed. The Company recorded $2.2 million, $2.7 million and $3.4 million in revenue related to the Rockefeller agreement during the years ended December 31, 2017, 2016 and 2015, respectively. Bristol-Myers Squibb Company (BMS) In 2014, the Company entered into a clinical trial collaboration with BMS to evaluate the safety, tolerability and preliminary efficacy of varlilumab and Opdivo®, BMS' PD-1 immune checkpoint inhibitor, in a Phase 1/2 study. Under the terms of this clinical trial collaboration, BMS made a one-time payment to the Company of $5.0 million and BMS and the Company amended the terms of the Company's existing license agreement with Medarex, which was acquired by BMS, related to the Company's CD27 program whereby certain future milestone payments were waived and future royalty rates were reduced that may have been due from the Company to Medarex. In return, BMS was granted a time-limited right of first negotiation if the Company wishes to out-license varlilumab. The companies also agreed to work exclusively with each other to explore anti-PD-1 antagonist antibody and anti-CD27 agonist antibody combination regimens. The clinical trial collaboration provides that the companies will share development costs and that the Company will be responsible for conducting the ongoing Phase 1/2 study. The Company has determined that its performance obligations under the BMS agreement, which primarily include performing research and development, supplying varlilumab and participating in the joint development committee, should be accounted for as a single unit of accounting and estimated that its performance period under the BMS agreement would be five years. Accordingly, the $5.0 million up-front payment was initially recorded as deferred revenue and is being recognized as revenue on a straight-line basis over the estimated five year performance period using the Contingency Adjusted Performance Model ("CAPM"). The BMS agreement also provides for BMS to reimburse the Company for 50% of the external costs incurred by the Company in connection with the clinical trial. These BMS payments are being recognized as revenue using the CAPM. The Company recorded $2.8 million, $2.1 million and $1.3 million in revenue related to the BMS agreement during the years ended December 31, 2017, 2016 and 2015, respectively. International AIDS Vaccine Initiative (IAVI) In 2017, the Company entered into an agreement with IAVI pursuant to which the Company performs research and development and manufacturing services for IAVI outlined under subsequently negotiated task orders. Revenue is recognized as services are performed under the negotiated task orders. The Company recorded $4.9 million in revenue related to the IAVI agreement during the year ended December 31, 2017. Frontier Biotechnologies, Inc. (Frontier) In 2017, the Company entered into an agreement with Frontier pursuant to which the Company performs research and development and manufacturing services for Frontier outlined under subsequently negotiated task orders. Revenue is recognized as services are performed under the negotiated task orders. The Company recorded $1.7 million in revenue related to the Frontier agreement during the year ended December 31, 2017.

Collaboration Agreements	12 Months Ended
Collaboration Agreements	Dec. 31, 2017
Collaboration Agreements
Collaboration Agreements	(13) Collaboration Agreements The Company has entered into license agreements whereby the Company has received licenses or options to license technology, specified patents or patent applications. The Company's licensing and development collaboration agreements generally provide for royalty payments equal to specified percentages of product sales, annual license maintenance fees, continuing patent prosecution costs and potential future milestone payments to third parties upon the achievement of certain developmental, regulatory and/or commercial milestones. Nonrefundable license fee expense of $0.7 million, $1.6 million and $0.9 million was recorded to research and development expense for the years ended December 31, 2017, 2016 and 2015, respectively. Medarex, Inc. (Medarex), which was acquired by Bristol-Myers Squibb The Company and Medarex have entered into an assignment and license agreement, as amended, that provides for the assignment of certain patent and other intellectual property rights and a license to certain Medarex technology related to the Company's APC Targeting Technology™ and an anti-mannose receptor product. Under the terms of the agreement, the Company may be required to pay royalties in the low-single digits on any net product sale of a licensed royalty-bearing product or anti-mannose product to Medarex until the later of (i) the expiration of the last to expire applicable patent and (ii) the tenth anniversary of the first commercial sale of such licensed product. Under a license agreement with Medarex, as amended, the Company acquired access to the UltiMab technology to develop and commercialize human antibodies to CD27, including varlilumab. The Company may be required to pay Medarex royalty payments in the low-to-mid single digits on any net product sales with respect to the development and commercialization of varlilumab until the later of (i) the expiration of the last to expire applicable patent and (ii) the tenth anniversary of the first commercial sale of such licensed product. Rockefeller University (Rockefeller) Under a license agreement with Rockefeller, the Company acquired the exclusive worldwide rights to human DEC-205 receptor, with the right to sublicense the technology. The license grant is exclusive except that Rockefeller may use and permit other nonprofit organizations to use the human DEC-205 receptor patent rights for educational and research purposes. The Company may be required to pay Rockefeller milestones of up to $3.8 million upon obtaining first approval for commercial sale in a first indication of a product targeting the licensed receptor and royalty payments in the low-to-mid single digits on any net product sales with respect to development and commercialization of the human DEC-205 receptor. University of Southampton, UK (Southampton) Under a license agreement with Southampton, the Company acquired the rights to develop human antibodies towards CD27, a potentially important target for immunotherapy of various cancers. The Company may be required to pay Southampton milestones of up to approximately $1.0 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low-single digits on any net product sales with respect to development and commercialization of varlilumab. Amgen Inc. (Amgen) Under a license agreement with Amgen, the Company acquired the exclusive rights to CDX-301 and CD40 ligand, or CD40L. CDX-301 and CD40L are immune modulating molecules that increase the numbers and activity of immune cells that control immune responses. The Company may be required to pay Amgen milestones of up to $0.9 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low-single digits on any net product sales with respect to development and commercialization of the technology licensed from Amgen, including CDX-301. Seattle Genetics, Inc. (Seattle Genetics) Under a license agreement with Seattle Genetics, the Company acquired the rights to proprietary ADC technology, with the right to sublicense, for use with the Company's proprietary antibodies for the potential treatment of cancer. The Company may be required to pay Seattle Genetics milestones of up to $5.0 million and $8.5 million for glembatumumab vedotin and CDX-014, respectively, upon obtaining first approval for commercial sale in a first indication and royalty payments in the mid-single digits on any net product sales with respect to development and commercialization of these drug candidates. Yale University (Yale) Under a license agreement with Yale, the Company may be required to make a one-time payment to Yale of $3.0 million with respect to each therapeutic or prophylactic RTK royalty-bearing product, including CDX-3379, that achieves a specified commercial milestone. In addition, the Company may be required to pay a low single-digit royalty on annual worldwide net sales of each RTK royalty-bearing product, including CDX-3379. MedImmune, LLC (MedImmune) Under an agreement with MedImmune, the Company has an exclusive license, with the right to sublicense, to specified patent rights and know-how that are controlled by MedImmune and relate to the research, development, manufacture and commercialization of CDX-3379. The Company may be required to pay Medimmune up to $45.0 million upon obtaining specified regulatory and development milestones in the first indication of CDX-3379. In addition, the Company may be required to pay MedImmune one-time milestone payments of up to $125.0 million if specified annual net sale thresholds are met related to the first indication of CDX-3379. The Company may also be required to pay MedImmune a tiered royalty on annual net sales of CDX-3379 at rates ranging from high single-digit to low teens percentages. The Company may also be required to pay specified royalties on annual net sales of CDX-3379 at a rate in the low single digits to certain other third parties from whom MedImmune licensed certain intellectual property.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Taxes

Income Taxes

(14) Income Taxes

The components of income tax benefit (provision) are as follows:

	Year Ended December 31,
	2017			2016			2015
	(In thousands)
Income Tax Benefit (Provision):
Federal	$	57,547		$	45,518		$	46,598
State		(2,479	)		7,268			10,642
Foreign		2,448			1,124			—
Income Tax Rate Change		(99,528	)		—			—
Expiration of Net Operating Losses and Research & Development Tax Credits		—			—			(155	)

		(42,012	)		53,910			57,085
Deferred Tax Valuation Allowance		66,294			(53,910	)		(57,085	)

	$	24,282		$	—		$	—

A reconciliation between the amount of reported income tax and the amount computed using the U.S. Statutory rate is as follows:

	2017			2016			2015
	(In thousands)
Pre-Tax Loss	$	(117,313	)	$	(128,530	)	$	(127,197	)


Loss at Statutory Rates		(39,887	)		(43,700	)		(43,247	)
Difference in Foreign Tax Rates		326			150			—
Research and Development Credits		(2,847	)		(5,203	)		(4,935	)
State Taxes		(6,283	)		(7,268	)		(10,642	)
Income Tax Rate Change		99,528			—			—
Other		(321	)		2,111			1,584
Recognition of APIC NOLs		(5,729	)		—			—
Impact of Pass-through Entities		(2,775	)		—			—
Expiration of Net Operating Losses and Research & Development Tax Credits		—			—			155
Change in Valuation Allowance		(66,294	)		53,910			57,085

Income Tax (Benefit) Provision	$	(24,282	)	$	—		$	—

Deferred tax assets and liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using future expected enacted rates. The principal components of the deferred tax assets and liabilities at December 31, 2017 and 2016, respectively, are as follows:

	December 31, 2017			December 31, 2016
	(In thousands)
Gross Deferred Tax Assets
Net Operating Loss Carryforwards	$	146,228		$	174,555
Foreign Net Operating Loss Carryforwards		3,572			1,124
Tax Credit Carryforwards		36,458			32,306
Deferred Research and Development Expenses		79,272			109,520
Stock-based Compensation		10,718			12,362
Fixed Assets		1,305			1,526
Deferred Revenue		686			1,418
Accrued Expenses and Other		316			894

		278,555			333,705
Gross Deferred Tax Liabilities
Other Acquired Intangibles		(1,792	)		(2,868	)
IPR&D Intangibles		(15,992	)		(28,054	)

Total Deferred Tax Assets and Liabilities		260,771			302,783

Valuation Allowance		(264,543	)		(330,837	)

Net Deferred Tax Liability	$	(3,772	)	$	(28,054	)

The Company has evaluated the positive and negative evidence bearing upon the realizability of its net deferred tax assets and considered its history of losses, ultimately concluding that it is "more likely than not" that the Company will not recognize the benefits of federal, state and foreign deferred tax assets and, as such, has maintained a full valuation allowance on its deferred tax assets.

During year ended December 31, 2017, the Company's gross deferred tax assets and corresponding valuation allowance each increased by $17.7 million. This was a one-time increase due to the adoption of a new accounting standard removing the requirement to recognize excess tax benefits from the exercise of stock options in additional paid-in-capital when realized.

On December 22, 2017, the Tax Cuts and Jobs Act ("TCJA") was enacted, leading to significant changes to U.S. tax law. Among other provisions, the TCJA lowered the U.S. federal corporate income tax rate from 35% to 21%, limited the deduction for net operating losses to 80% of taxable income while providing that net operating loss carryovers for years after 2017 will not expire, imposed a mandatory one-time transition tax on previously deferred foreign earnings and eliminated or reduced certain income tax deductions. Also on December 22, 2017, the SEC staff issued SAB 118, allowing companies to record the effects of the TCJA on a provisional basis during a measurement period not to extend beyond one year of the enactment date.

As a result of the TCJA, the Company revalued its deferred tax liabilities at the new federal rate of 21%, resulting in a $6.9 million decrease and a corresponding income tax benefit. The Company also scheduled out reversals of its deferred tax assets and liabilities, determining that their reversal would create future indefinite-lived net operating losses under the TCJA. As such, the valuation allowance was reduced relating to the remaining indefinite-lived federal deferred tax liabilities balance, leading to an additional income tax benefit of $12.2 million. The Company's deferred tax asset balance was also revalued at the new 21% rate resulting in a $99.5 million decrease in the balance with a corresponding decrease to the valuation allowance. Finally, the one-time transition tax on previously deferred foreign earnings under the TCJA is not expected to impact the Company due to a net deficit in the Australian subsidiary.

In accordance with SAB 118, the Company considers the aforementioned adjustments related to the TCJA to be provisional amounts based on the Company's best estimates at December 31, 2017. Updated guidance, interpretations or assumptions could lead the Company to make further adjustments to income tax benefit (provision) in the future. The Company expects its accounting for the tax effects of the TCJA to be completed in 2018.

The net deferred tax liability of $3.8 million and $28.1 million at December 31, 2017 and 2016, respectively, relates to the temporary differences associated with the IPR&D intangible assets acquired in previous business combinations and are not deductible for tax purposes. The Company recorded an income tax benefit of $5.2 million during the year ended December 31, 2017 due to a decrease in deferred tax liabilities resulting from the partial impairment of the anti-KIT program.

As of December 31, 2017, the Company had federal and state net operating loss carryforwards of $561.8 million and $435.9 million, respectively, which may be available to offset certain future income tax liabilities and begin to expire in 2018 and 2028, respectively. As of December 31, 2017, the Company also had federal and state research and development tax credit carryforwards of $29.0 million and $9.5 million, respectively, which may be available to offset future income tax liabilities and begin to expire in 2018 and 2017, respectively.

Utilization of the net operating loss carryforwards and research and credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, or Section 382, due to ownership changes that occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has estimated the amounts of net operating loss and research and development tax credit carryforwards which will expire unutilized as a result of its estimated annual limitations under Section 382 and has excluded those amounts from the carryforward amounts disclosed above and in the deferred tax assets and liabilities table included in this footnote. The Company has concluded Section 382 studies through 2015 for Celldex generated NOLs.

The Company incurred a foreign pre-tax loss of $8.2 million and $3.7 million during the years ended December 31, 2017 and 2016, respectively. Beginning with the 2016 tax returns, the Company elected to classify the Australian entity as a disregarded entity for income tax purposes. The foreign pre-tax losses have been included with the Federal net operating loss carryforwards.

As of December 31, 2017 and 2016, the Company did not have any unrecognized tax benefits.

Massachusetts, New Jersey, Connecticut and Australia are the jurisdictions in which the Company primarily operates or has operated and has income tax nexus. The Company is not currently under examination by these or any other jurisdictions for any tax year. Generally, in U.S. federal and state taxing jurisdictions, all years which generated net operating losses and/or tax credit carryforwards remain subject to examination to the extent those carryforwards are utilized in a subsequent period.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies

Commitments and Contingencies

(15) Commitments and Contingencies

The Company has facility and equipment leases that expire at various dates through 2020. Certain of these facility leases contain renewal options, early termination provisions, and provisions that escalate the base rent payments and require the Company to pay common area maintenance costs ("CAM") during the lease term. The following obligations for base rent and CAM costs under facility and other non-cancelable operating leases as of December 31, 2017 do not include the exercise of renewal terms or early termination provisions (in thousands):

2018	$	4,591
2019		4,472
2020		2,498
2021		—
2022		—
Thereafter		—

Total minimum lease payments	$	11,561

The Company's total rent and CAM expense for all facility leases was $4.1 million, $4.8 million and $2.9 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Retirement Savings Plan	12 Months Ended
Retirement Savings Plan	Dec. 31, 2017
Retirement Savings Plan
Retirement Savings Plan	(16) Retirement Savings Plan The Company maintains a 401(k) Plan which is available to substantially all employees. Under the terms of the 401(k) Plan, participants may elect to contribute up to 60% of their compensation or the statutory prescribed limits. The Company may make 50% matching contributions on up to 4% of a participant's annual salary. Benefit expense for the 401(k) Plan was $0.5 million for the year ended December 31, 2017 and $0.4 million for each of the years ended December 31, 2016 and 2015.

Kolltan Acquisition

12 Months Ended

Dec. 31, 2017

Kolltan Acquisition

Kolltan Acquisition

(17) Kolltan Acquisition

On November 29, 2016, the Company acquired all of the share and debt interests of Kolltan Pharmaceuticals, Inc. ("Kolltan"), a clinical-stage biopharmaceutical company, in exchange for 18,257,996 shares of the Company's common stock plus contingent consideration in the form of development and approval milestones up to a maximum of $172.5 million. The Company completed this acquisition in order to gain access to Kolltan's antibody-based drug development programs targeting receptor tyrosine kinases (RTKs) for the treatment of cancer and other diseases with significant unmet needs.

Purchase Price

The purchase price for Kolltan was calculated based on the closing price of the Company's common stock of $4.02 per share on November 29, 2016. The Company also recorded a liability of $44.2 million which represented the initial fair value of the contingent consideration. This fair value measurement used significant unobservable inputs representing a Level 3 measurement more fully described in Note 4, Fair Value Measurements to these consolidated financial statements. Subsequent changes to the fair value of the contingent consideration will be recognized as adjustments to operating earnings. The acquisition was accounted for using the acquisition method of accounting which requires all assets acquired and liabilities assumed recognized at their acquisition-date fair values.

The total consideration transferred consisted of the following (in thousands):

Fair value of common stock issued for upfront payment	$	73,397
Fair value of contingent consideration		44,200
Kolltan transaction expenses paid in cash by the Company		3,768

Total consideration transferred	$	121,365

Allocations of Assets and Liabilities

The purchase price allocation was finalized in the fourth quarter of 2017 with no adjustments made to the initial purchase price allocation. The following table summarizes the fair values of the assets acquired and liabilities assumed as of November 29, 2016 (in thousands):

Cash and cash equivalents	$	8,160
Other current and long-term assets		799
Property and equipment, net		2,072
In-process research and development (IPR&D)		61,690
Goodwill		82,011
Deferred tax liabilities, net		(23,393	)
Other assumed liabilities		(9,974	)

Total	$	121,365

IPR&D primarily represents the initial estimated fair value of $40.0 million, $3.5 million and $18.0 million for the anti-KIT program, CDX-3379 and TAM programs, respectively, using probability adjusted discounted cash flow analyses. The expected future net cash flows for the anti-KIT program, CDX-3379 and TAM programs were based on the expectation that a Biologics License Application ("BLA") would be filed with the FDA no earlier than the end of 2023, 2024 and 2028, respectively, with an expected commercial launch as promptly as practicable after necessary regulatory approvals are received. The estimated development costs included in the expected future net cash flows were approximately $132 million combined.

The deferred tax liability, net of $23.4 million primarily relates to the temporary differences associated with the IPR&D intangible assets, which are not deductible for tax purposes.

The excess of purchase price over the fair value amounts assigned to the identifiable assets acquired and liabilities assumed represents the goodwill amount resulting from the acquisition. The value of the goodwill can be attributable to the synergies related to the combined antibody-based platform and a deferred tax liability related to acquired IPR&D intangible assets. None of the goodwill is expected to be deductible for income tax purposes.

Acquisition-Related Expenses, Including Severance

The Company incurred $0.7 million in acquisition-related expenses in the consolidated statements of operations for the year ended December 31, 2016. From the acquisition date through December 31, 2016, the consolidated statements of operations also include $2.4 and $0.7 million in Kolltan related severance expense within general and administrative and research and development expenses, respectively.

Pro Forma Financial Information

The operating results of Kolltan and pro forma adjustments including severance expense and transaction expenses of $3.1 million and $0.7 million, respectively, have been included in the accompanying consolidated financial statements from November 29, 2016 to December 31, 2016. Kolltan had no revenues from November 29, 2016 through December 31, 2016. The following unaudited pro forma financial summary is presented as if the operations of the Company and Kolltan were combined as of January 1, 2015. The unaudited pro forma combined results are not necessarily indicative of the actual results that would have occurred had the acquisition been consummated at that date or of the future operations of the combined entities.

	Unaudited Years Ended December 31,
	2016			2015
	(In thousands)
Revenue	$	6,786		$	5,480
Net loss	$	(146,905	)	$	(157,690	)
Basic and diluted net loss per common share	$	(1.24	)	$	(1.37	)

- Definition

The entire disclosure for a business combination (or series of individually immaterial business combinations) completed during the period, including background, timing, and recognized assets and liabilities. The disclosure may include leverage buyout transactions (as applicable).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1497-128463

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 805
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
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Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=73530397&loc=d3e4934-128472

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=73530397&loc=d3e4926-128472

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 4A
-URI http://asc.fasb.org/extlink&oid=73530397&loc=SL65897772-128472

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1383-128463

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6996-128479

+ Details

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2017

Selected Quarterly Financial Data (Unaudited)

Selected Quarterly Financial Data (Unaudited)

(18) Selected Quarterly Financial Data (Unaudited)

2017	Q1 2017			Q2 2017			Q3 2017			Q4 2017
	(In thousands, except per share amounts)
Total revenue	$	1,534		$	3,829		$	3,924		$	3,456
Net loss		(34,261	)		(28,566	)		(26,363	)		(3,841	)
Basic and diluted net loss per common share		(0.28	)		(0.23	)		(0.20	)		(0.03	)

2016	Q1 2016			Q2 2016			Q3 2016			Q4 2016
	(In thousands, except per share amounts)
Total revenue	$	1,303		$	1,389		$	2,220		$	1,874
Net loss		(34,673	)		(31,952	)		(29,598	)		(32,307	)
Basic and diluted net loss per common share		(0.35	)		(0.32	)		(0.29	)		(0.30	)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Summary of Significant Accounting Policies

Basis of Presentation

Use of Estimates

Cash and Cash Equivalents

Marketable Securities

Concentration of Credit Risk and of Significant Customers and Suppliers

Fair Value Measurements

Level 3: Unobservable inputs based on the Company's assessment of the assumptions that market participants would use in pricing the asset or liability.

Property and Equipment

Other Assets

Business Combinations

Intangible Assets

Goodwill

Impairment of Intangible and Long-Lived Assets

Revenue Recognition

Research and Development Expenses

Patent Costs

Stock-Based Compensation

Foreign Currency Translation

Income Taxes

Comprehensive Loss

Net Loss Per Share

	Year Ended December 31,
	2017		2016		2015
Stock options		10,856,212		10,218,710		8,110,239
Restricted stock		96,668		50,000		19,500

		10,952,880		10,268,710		8,129,739

Newly-Adopted Accounting Pronouncements

Recent Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Significant Accounting Policies

Schedule of potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive

	Year Ended December 31,
	2017		2016		2015
Stock options		10,856,212		10,218,710		8,110,239
Restricted stock		96,668		50,000		19,500

		10,952,880		10,268,710		8,129,739

Accumulated Other Comprehensive Income (Tables)

12 Months Ended

Dec. 31, 2017

Accumulated Other Comprehensive Income

Summary of changes in accumulated other comprehensive income

	Unrealized Gain (Loss) on Marketable Securities			Foreign Currency Items		Total
	(In thousands)
Balance at December 31, 2016	$	(55	)	$	2,596	$	2,541
Other comprehensive gain		23			—		23

Balance at December 31, 2017	$	(32	)	$	2,596	$	2,564

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Measurements

Schedule of financial assets and liabilities subject to fair value measurements

	As of December 31, 2017		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	24,061		—	$	24,061		—
Marketable securities		99,139		—		99,139		—

	$	123,200		—	$	123,200		—


Liabilities:
Kolltan acquisition contingent consideration	$	43,400		—		—	$	43,400

	$	43,400		—		—	$	43,400

	As of December 31, 2016		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	20,445		—	$	20,445		—
Marketable securities		147,315		—		147,315		—

	$	167,760		—	$	167,760		—


Liabilities:
Kolltan acquisition contingent consideration	$	44,200		—		—	$	44,200

	$	44,200		—		—	$	44,200

Schedule of the Company's contingent consideration liabilities measured at fair value using Level 3 inputs

The following table reflects the activity for the Company's contingent consideration liabilities measured at fair value using Level 3 inputs for the year ended December 31, 2017 (in thousands):

	Other Liabilities: Contingent Consideration
Balance at December 31, 2016	$	44,200
Fair value adjustments included in operating expenses		(800	)

Balance at December 31, 2017	$	43,400

Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Marketable Securities

Summary of marketable securities, classified as available-for-sale

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(In thousands)
December 31, 2017
Marketable securities
U.S. government and municipal obligations
Maturing in one year or less	$	26,164	$	3	$	(9	)	$	26,158
Maturing after one year through three years		—		—		—			—

Total U.S. government and municipal obligations	$	26,164	$	3	$	(9	)	$	26,158

Corporate debt securities
Maturing in one year or less	$	73,007	$	1	$	(27	)	$	72,981
Maturing after one year through three years		—		—		—			—

Total corporate debt securities	$	73,007	$	1	$	(27	)	$	72,981

Total marketable securities	$	99,171	$	4	$	(36	)	$	99,139


December 31, 2016
Marketable securities
U.S. government and municipal obligations
Maturing in one year or less	$	52,754	$	5	$	(12	)	$	52,747
Maturing after one year through three years		296		8		—			304

Total U.S. government and municipal obligations	$	53,050	$	13	$	(12	)	$	53,051

Corporate debt securities
Maturing in one year or less	$	94,320	$	—	$	(56	)	$	94,264
Maturing after one year through three years		—		—		—			—

Total corporate debt securities	$	94,320	$	—	$	(56	)	$	94,264

Total marketable securities	$	147,370	$	13	$	(68	)	$	147,315

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2017

Property and Equipment, Net

Schedule of property and equipment

	December 31, 2017			December 31, 2016
	(In thousands)
Laboratory Equipment	$	7,770		$	6,771
Manufacturing Equipment		4,354			4,312
Office Furniture and Equipment		3,764			3,677
Leasehold Improvements		17,164			17,115
Construction in Progress		932			1,283

Total Property and Equipment		33,984			33,158
Less: Accumulated Depreciation and Amortization		(23,612	)		(19,966	)

Property and Equipment, Net	$	10,372		$	13,192

Intangible Assets and Goodwill (Tables)

12 Months Ended

Dec. 31, 2017

Intangible Assets and Goodwill

Schedule of finite-lived intangible assets subject to amortization and indefinite-lived assets

		December 31, 2017							December 31, 2016
	Estimated Life	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
		(In thousands)
Finite-lived Intangible Assets:
License Rights	16 years	$	14,500	$	(7,399	)	$	7,101	$	14,500	$	(6,503	)	$	7,997

Indefinite-lived Intangible Assets:
IPR&D	Indefinite		60,490		—			60,490		73,490		—			73,490

Total Intangible Assets, Net		$	74,990	$	(7,399	)	$	67,591	$	87,990	$	(6,503	)	$	81,487

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2017

Accrued Expenses

Schedule of accrued expenses

	December 31, 2017		December 31, 2016
	(In thousands)
Accrued Payroll and Employee Benefits	$	6,348	$	7,132
Accrued Research and Development Contract Costs		11,399		17,742
Accrued Professional Fees		1,408		1,146
Other Accrued Expenses		300		2,637

	$	19,455	$	28,657

Other Long-Term Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Other Long-Term Liabilities

Schedule of other long-term liabilities

	December 31, 2017			December 31, 2016
	(In thousands)
Net Deferred Tax Liabilities Related to IPR&D (Note 14)	$	3,772		$	28,054
Deferred Income From Sale of Tax Benefits		6,756			9,436
Other		1,344			2,091
Contingent Milestones (Note 4)		43,400			44,200
Deferred Revenue		2,813			3,749

Total		58,085			87,530
Less Current Portion		(6,566	)		(4,826	)

Long-Term Portion	$	51,519		$	82,704

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Stock-Based Compensation

Summary of stock option activity

	Shares			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at December 31, 2016		10,218,710		$	11.14		6.5
Granted		2,427,200		$	2.37
Exercised		—		$	—
Canceled		(1,789,698	)	$	9.76

Options Outstanding at December 31, 2017		10,856,212		$	9.40		6.1


Options Vested and Expected to Vest at December 31, 2017		10,780,023		$	9.43		6.1
Options Exercisable at December 31, 2017		6,846,254		$	11.18		4.5
Shares Available for Grant Under the 2008 Plan		8,324,310

Summary of restricted stock activity

	Shares			Weighted Average Grant Date Fair Value (per share)
Outstanding and unvested at December 31, 2016		50,000		$	4.72
Granted		70,000		$	2.32
Vested		(16,665	)	$	4.72
Canceled		(6,667	)	$	4.72

Outstanding and unvested at December 31, 2017		96,668		$	2.98

Schedule of stock-based compensation expense

	2017		2016		2015
	(In thousands)
Research and development	$	6,693	$	7,821	$	6,186
General and administrative		5,619		7,496		6,588

Total stock-based compensation expense	$	12,312	$	15,317	$	12,774

Schedule of assumptions used for the fair value of employee stock options granted

	2017	2016	2015
Expected stock price volatility	75 - 77%	70 - 77%	67 - 69%
Expected option term	6.0 Years	6.0 Years	6.0 Years
Risk-free interest rate	2.0 - 2.3%	1.4 - 2.3%	1.8 - 2.2%
Expected dividend yield	None	None	None

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Taxes

Schedule of components of income tax benefit (provision)

	Year Ended December 31,
	2017			2016			2015
	(In thousands)
Income Tax Benefit (Provision):
Federal	$	57,547		$	45,518		$	46,598
State		(2,479	)		7,268			10,642
Foreign		2,448			1,124			—
Income Tax Rate Change		(99,528	)		—			—
Expiration of Net Operating Losses and Research & Development Tax Credits		—			—			(155	)

		(42,012	)		53,910			57,085
Deferred Tax Valuation Allowance		66,294			(53,910	)		(57,085	)

	$	24,282		$	—		$	—

Schedule of reconciliation between the amount of reported income tax and the amount computed using the U.S. Statutory rate

	2017			2016			2015
	(In thousands)
Pre-Tax Loss	$	(117,313	)	$	(128,530	)	$	(127,197	)


Loss at Statutory Rates		(39,887	)		(43,700	)		(43,247	)
Difference in Foreign Tax Rates		326			150			—
Research and Development Credits		(2,847	)		(5,203	)		(4,935	)
State Taxes		(6,283	)		(7,268	)		(10,642	)
Income Tax Rate Change		99,528			—			—
Other		(321	)		2,111			1,584
Recognition of APIC NOLs		(5,729	)		—			—
Impact of Pass-through Entities		(2,775	)		—			—
Expiration of Net Operating Losses and Research & Development Tax Credits		—			—			155
Change in Valuation Allowance		(66,294	)		53,910			57,085

Income Tax (Benefit) Provision	$	(24,282	)	$	—		$	—

Schedule of principal components of the deferred tax assets and liabilities

	December 31, 2017			December 31, 2016
	(In thousands)
Gross Deferred Tax Assets
Net Operating Loss Carryforwards	$	146,228		$	174,555
Foreign Net Operating Loss Carryforwards		3,572			1,124
Tax Credit Carryforwards		36,458			32,306
Deferred Research and Development Expenses		79,272			109,520
Stock-based Compensation		10,718			12,362
Fixed Assets		1,305			1,526
Deferred Revenue		686			1,418
Accrued Expenses and Other		316			894

		278,555			333,705
Gross Deferred Tax Liabilities
Other Acquired Intangibles		(1,792	)		(2,868	)
IPR&D Intangibles		(15,992	)		(28,054	)

Total Deferred Tax Assets and Liabilities		260,771			302,783

Valuation Allowance		(264,543	)		(330,837	)

Net Deferred Tax Liability	$	(3,772	)	$	(28,054	)

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies

Schedule of obligations for base rent and CAM costs under facility and other non-cancelable operating leases

The following obligations for base rent and CAM costs under facility and other non-cancelable operating leases as of December 31, 2017 do not include the exercise of renewal terms or early termination provisions (in thousands):

2018	$	4,591
2019		4,472
2020		2,498
2021		—
2022		—
Thereafter		—

Total minimum lease payments	$	11,561

Kolltan Acquisition (Tables)

12 Months Ended

Dec. 31, 2017

Kolltan Acquisition

Schedule of acquisition-date fair value of the consideration transferred

The total consideration transferred consisted of the following (in thousands):

Fair value of common stock issued for upfront payment	$	73,397
Fair value of contingent consideration		44,200
Kolltan transaction expenses paid in cash by the Company		3,768

Total consideration transferred	$	121,365

Summary of fair values of the assets acquired and liabilities assumed at the acquisition date

The following table summarizes the fair values of the assets acquired and liabilities assumed as of November 29, 2016 (in thousands):

Cash and cash equivalents	$	8,160
Other current and long-term assets		799
Property and equipment, net		2,072
In-process research and development (IPR&D)		61,690
Goodwill		82,011
Deferred tax liabilities, net		(23,393	)
Other assumed liabilities		(9,974	)

Total	$	121,365

Schedule of the unaudited pro forma financial information

	Unaudited Years Ended December 31,
	2016			2015
	(In thousands)
Revenue	$	6,786		$	5,480
Net loss	$	(146,905	)	$	(157,690	)
Basic and diluted net loss per common share	$	(1.24	)	$	(1.37	)

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Selected Quarterly Financial Data (Unaudited)

Schedule of selected quarterly financial data (unaudited)

2017	Q1 2017			Q2 2017			Q3 2017			Q4 2017
	(In thousands, except per share amounts)
Total revenue	$	1,534		$	3,829		$	3,924		$	3,456
Net loss		(34,261	)		(28,566	)		(26,363	)		(3,841	)
Basic and diluted net loss per common share		(0.28	)		(0.23	)		(0.20	)		(0.03	)

2016	Q1 2016			Q2 2016			Q3 2016			Q4 2016
	(In thousands, except per share amounts)
Total revenue	$	1,303		$	1,389		$	2,220		$	1,874
Net loss		(34,673	)		(31,952	)		(29,598	)		(32,307	)
Basic and diluted net loss per common share		(0.35	)		(0.32	)		(0.29	)		(0.30	)

Nature of Business and Overview - (Details) $ in Thousands	3 Months Ended								12 Months Ended
Nature of Business and Overview - (Details) $ in Thousands	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) Program product	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Nature of Business and Overview
Number of drug candidates in clinical development \| product									7
Cash, cash equivalents and marketable securities	$ 139,400								$ 139,400
Net Loss	$ (3,841)	$ (26,363)	$ (28,566)	$ (34,261)	$ (32,307)	$ (29,598)	$ (31,952)	$ (34,673)	(93,031)	$ (128,530)	$ (127,197)
Net cash used in operations									$ 99,931	$ 113,036	$ 98,887
Minimum number of programs at risk due to fund restriction \| Program									1

Summary of Significant Accounting Policies - Basis of Presentation (Details)	12 Months Ended
	Dec. 31, 2017 segment
Summary of Significant Accounting Policies
Operating segments (in segments)	1

Summary of Significant Accounting Policies - Concentration of Credit Risk- (Details) - Revenue - Customer concentration	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Combined IAVI, Frontier and BMS
Concentration risk
Concentration risk (as a percent)	73.00%
Combined Rockefeller and BMS
Concentration risk
Concentration risk (as a percent)		71.00%	86.00%

Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Laboratory Equipment
Property and Equipment
Estimated useful lives	5 years
Office Furniture and Equipment
Property and Equipment
Estimated useful lives	5 years
Computer Equipment
Property and Equipment
Estimated useful lives	3 years
Manufacturing Equipment \| Minimum
Property and Equipment
Estimated useful lives	7 years
Manufacturing Equipment \| Maximum
Property and Equipment
Estimated useful lives	10 years

Summary of Significant Accounting Policies - Other Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Summary of Significant Accounting Policies
Other assets including non-controlling investment	$ 1.8	$ 1.8

Summary of Significant Accounting Policies - Intangible Assets (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Summary of Significant Accounting Policies
Impairment charges of intangible assets	$ 13,000

Summary of Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Thousands		12 Months Ended
	Jul. 01, 2017	Dec. 31, 2017
Summary of Significant Accounting Policies
Changes to carrying amount of goodwill	$ 0	$ 0

Summary of Significant Accounting Policies - Foreign Currency Translation (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Summary of Significant Accounting Policies
Unrealized gain related to foreign currency translation included in AOCI	$ 2.6	$ 2.6

Summary of Significant Accounting Policies - Dilutive Common Shares (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net loss per share
Potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive	10,952,880	10,268,710	8,129,739
Stock options
Net loss per share
Potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive	10,856,212	10,218,710	8,110,239
Restricted stock
Net loss per share
Potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive	96,668	50,000	19,500

Summary of Significant Accounting Policies - Newly-Adopted Accounting Pronouncements (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2017	Dec. 31, 2017
Newly-Adopted Accounting Pronouncements
Increase in deferred tax and valuation allowance		$ 17.7
Adjustments for New Accounting Principle, Early Adoption \| Accounting Standards Update
Newly-Adopted Accounting Pronouncements
Increase in deferred tax and valuation allowance	$ 17.7

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income
Amounts reclassified from other comprehensive income	$ 0	$ 0	$ 0
Period Start Balance	265,431	290,105	211,660
Period End Balance	236,369	265,431	290,105
Unrealized Gain (Loss) on Marketable Securities
Accumulated Other Comprehensive Income
Period Start Balance	(55)
Other comprehensive gain	23
Period End Balance	(32)	(55)
Foreign Currency Items
Accumulated Other Comprehensive Income
Period Start Balance	2,596
Period End Balance	2,596	2,596
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income
Period Start Balance	2,541	2,307	2,590
Other comprehensive gain	23
Period End Balance	$ 2,564	$ 2,541	$ 2,307

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair value \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	$ 43,400	$ 44,200
Fair Value Measurements \| Level 2
Assets:
Money market funds and cash equivalents	24,061	20,445
Marketable securities	99,139	147,315
Total financial assets at fair value	123,200	167,760
Fair Value Measurements \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	43,400	44,200
Total financial liabilities at fair value	43,400	44,200
Fair Value Measurements \| Fair value
Assets:
Money market funds and cash equivalents	24,061	20,445
Marketable securities	99,139	147,315
Total financial assets at fair value	123,200	167,760
Liabilities:
Kolltan acquisition contingent consideration	43,400	44,200
Total financial liabilities at fair value	$ 43,400	$ 44,200

Fair Value Measurements - Contingent Consideration Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Roll-forward of acquisition-related contingent consideration
Fair value adjustments included in operating expenses	$ (800)
Fair value \| Level 3
Roll-forward of acquisition-related contingent consideration
Balance at beginning of period	44,200
Fair value adjustments included in operating expenses	(800)
Balance at end of period	$ 43,400

Fair Value Measurements - Additional information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Nov. 29, 2016
Fair value measurements
Gain on Fair Value Remeasurement of Contingent Consideration	$ 800
Kolltan \| Specified development, regulatory approvals or sales-based milestones
Fair value measurements
Milestone payments			$ 172,500
Fair value
Fair value measurements
Assets level 1 to level 2 transfers	0	$ 0
Assets level 2 to level 1 transfers	0	0
Liabilities level 1 to level 2 transfers	0	0
Liabilities level 2 to level 1 transfers	0	0
Asset transfer out of level 3	0	0
Asset transfer into level 3	0	0
Liabilities transfers out of level 3	0	0
Liabilities transfers into level 3	$ 0	$ 0

Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized Cost
Amortized cost	$ 99,171	$ 147,370
Gross Unrealized Gains
Gross Unrealized Gains	4	13
Gross Unrealized Losses
Gross Unrealized Losses	(36)	(68)
Fair Value
Fair Value	99,139	147,315
Other-than-temporarily impairment	0
Accrued interest	300	600
U.S. government and municipal obligations
Amortized Cost
Maturing in one year or less	26,164	52,754
Maturing after one year through three years		296
Amortized cost	26,164	53,050
Gross Unrealized Gains
Maturing in one year or less	3	5
Maturing after one year through three years		8
Gross Unrealized Gains	3	13
Gross Unrealized Losses
Maturing in one year or less	(9)	(12)
Gross Unrealized Losses	(9)	(12)
Fair Value
Maturing in one year or less	26,158	52,747
Maturing after one year through three years		304
Fair Value	26,158	53,051
Corporate debt securities
Amortized Cost
Maturing in one year or less	73,007	94,320
Amortized cost	73,007	94,320
Gross Unrealized Gains
Maturing in one year or less	1
Gross Unrealized Gains	1
Gross Unrealized Losses
Maturing in one year or less	(27)	(56)
Gross Unrealized Losses	(27)	(56)
Fair Value
Maturing in one year or less	72,981	94,264
Fair Value	$ 72,981	$ 94,264

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property and Equipment
Total Property and Equipment	$ 33,984	$ 33,158
Less Accumulated Depreciation and Amortization	(23,612)	(19,966)
Property and Equipment, Net	10,372	13,192
Depreciation and amortization expense	4,414	3,095	$ 2,998
Laboratory Equipment
Property and Equipment
Total Property and Equipment	7,770	6,771
Manufacturing Equipment
Property and Equipment
Total Property and Equipment	4,354	4,312
Office Furniture and Equipment
Property and Equipment
Total Property and Equipment	3,764	3,677
Leasehold Improvements
Property and Equipment
Total Property and Equipment	17,164	17,115
Construction in Progress
Property and Equipment
Total Property and Equipment	$ 932	$ 1,283

Intangible Assets and Goodwill - Intangible Assets, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-lived intangible asset
Accumulated Amortization	$ (7,399)	$ (6,503)
Total Intangible Assets
Gross carrying amount of total intangible assets, net	74,990	87,990
Net carrying amount of total intangible assets, net	67,591	81,487
In-Process Research and Development Impairment	$ 13,000
License Rights
Finite-lived intangible asset
Estimated Life	16 years
Gross carrying amount finite-lived	$ 14,500	14,500
Accumulated Amortization	(7,399)	(6,503)
Net carrying amount finite-lived	7,101	7,997
IPR&D
Indefinite-lived intangible assets:
Indefinite-lived intangible assets	60,490	73,490
Net carrying amount of indefinite-lived	$ 60,490	$ 73,490

Intangible Assets and Goodwill - Amortization expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Intangible Assets and Goodwill
Amortization expense for intangible assets	$ 896	$ 997	$ 1,013
Estimated future amortization expense of intangible assets
2018	900
2019	900
2020	900
2021	900
2022	$ 900

Intangible Assets and Goodwill - Goodwill (Details) - USD ($) $ in Thousands		12 Months Ended
	Jul. 01, 2017	Dec. 31, 2017
Intangible Assets and Goodwill
Changes to carrying amount of goodwill	$ 0	$ 0

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Expenses
Accrued Payroll and Employee Benefits	$ 6,348	$ 7,132
Accrued Research and Development Contract Costs	11,399	17,742
Accrued Professional Fees	1,408	1,146
Other Accrued Expenses	300	2,637
Accrued Expenses	$ 19,455	$ 28,657

Other Long-Term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other Long-Term Liabilities
Net Deferred Tax Liabilities related to IPR&D (Note 14)	$ 3,772	$ 28,054
Deferred Income from Sale of Tax Benefits	6,756	9,436
Other	1,344	2,091
Contingent Milestones (Note 4)	43,400	44,200
Deferred Revenue	2,813	3,749
Total	58,085	87,530
Less Current Portion	(6,566)	(4,826)
Long-Term Portion	$ 51,519	$ 82,704

Other Long-Term Liabilities- New Jersey tax benefits (Details) - USD ($) $ in Thousands	1 Months Ended				12 Months Ended
	Nov. 30, 2015	Dec. 31, 2014	Jan. 31, 2014	Jan. 31, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment and other income					$ 4,214	$ 4,386	$ 2,344
New Jersey tax benefits
Amount of tax benefit	$ 9,800	$ 1,900	$ 1,100	$ 800
Proceeds from sale of tax credits	$ 9,200	$ 1,800	$ 1,000	$ 800
Base of operations requirement (in years)					5 years
Investment and other income					$ 2,700	$ 2,800	$ 1,000

Stockholders' Equity - Common Stock (Details) - USD ($) $ in Thousands	1 Months Ended		2 Months Ended	12 Months Ended
	Nov. 30, 2017	May 31, 2016	Feb. 28, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 13, 2017
Common Stock
Maximum aggregate offering price of securities available for sale							$ 250,000
Aggregate offering price stock sale		$ 60,000
Additional offering price stock sale authorized	$ 75,000
Net proceeds from sale of common stock				$ 51,025	$ 13,946	$ 188,840
Common Stock
Common Stock
Shares Issued in Connection with Cantor Agreement (in shares)				17,722,863	3,303,800
Aggregate gross offering price available				$ 67,600
Common stock issued (in shares)			2,401,847			8,337,500
Net proceeds from sale of common stock			$ 6,100

Stockholders' Equity - Convertible Preferred Stock (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
Preferred stock, shares authorized	3,000,000	3,000,000
Preferred stock, shares outstanding	0	0
Series C-1 Preferred Stock
Preferred stock, shares authorized	350,000
Preferred stock, shares outstanding	0	0

Stock-Based Compensation - Employee Stock Purchase Plan (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Celldex Research 2005 Plan
Stock-Based Compensation
Available for issuance (in shares)	0
2004 ESSP Plan
Stock-Based Compensation
Common stock reserved for issuance (in shares)	400,000
Purchase price of fair value of common stock (in percent)	85.00%
Issued (in shares)	80,379	59,335	15,755
Available for issuance (in shares)	197,857

Stock-Based Compensation - Employee Stock Option and Incentive Plan (Details) - 2008 Plan	12 Months Ended
	Dec. 31, 2017 shares
Stock-Based Compensation
Common stock authorized grants (in shares)	20,000,000
Vesting period (in years)	4 years
Expiration period (in years)	10 years
Threshold percentage of voting stock	10.00%
Principal Owner
Stock-Based Compensation
Expiration period (in years)	5 years
Exercise price as a percentage of fair market value	110.00%

Stock-Based Compensation - Employee Stock Option and Incentive Plan Activity (Details) - 2008 Plan - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares
Options Outstanding at beginning of the period (in shares)	10,218,710
Granted (in shares)	2,427,200
Canceled (in shares)	(1,789,698)
Options Outstanding at the end of the period (in shares)	10,856,212	10,218,710
Options Vested and Expected to Vest at the end of the period (in shares)	10,780,023
Options Exercisable at the end of the period (in shares)	6,846,254
Shares Available for Grant (in shares)	8,324,310
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 11.14
Granted (in dollars per share)	2.37
Canceled (in dollars per share)	9.76
Options Outstanding at the end of the period (in dollars per share)	9.40	$ 11.14
Options Vested and Expected to Vest at the end of the period (in dollars per share)	9.43
Options Exercisable at the end of the period (in dollars per share)	$ 11.18
Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at the end of the period	6 years 1 month 6 days	6 years 6 months
Options Vested and Expected to Vest at the end of the period	6 years 1 month 6 days
Options Exercisable at the end of the period	4 years 6 months

Stock-Based Compensation - Employee Stock Option and Incentive Plan Activity Additional Information (Details) - 2008 Plan - Stock options - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Additional information
Intrinsic value of options exercised	$ 0.0	$ 0.1	$ 14.4
Weighted average grant-date fair value (in dollars per share)	$ 1.58	$ 3.18	$ 15.25
Fair value of options vested	$ 13.4	$ 17.0	$ 10.0
Intrinsic value of options outstanding	1.1
Intrinsic value of options vested and expected to vest	1.1
Compensation cost not yet recognized	$ 15.0
Weighted average period compensation cost is expected to be recognized (in years)	2 years 8 months 12 days

Stock-Based Compensation - Restricted Stock (Details) - 2008 Plan - Restricted stock	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Shares
Outstanding and unvested at the beginning of the period (in shares) \| shares	50,000
Granted (in shares) \| shares	70,000
Vested (in shares) \| shares	(16,665)
Canceled (in shares) \| shares	(6,667)
Outstanding and unvested at the end of the period (in shares) \| shares	96,668
Weighted Average Grant Date Fair Value (per share)
Outstanding and unvested at the beginning of the period (in dollars per share) \| $ / shares	$ 4.72
Granted (in dollars per share) \| $ / shares	2.32
Vested (in dollars per share) \| $ / shares	4.72
Canceled (in dollars per share) \| $ / shares	4.72
Outstanding and unvested at the end of the period (in dollars per share) \| $ / shares	$ 2.98

Stock-Based Compensation - Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-based compensation expense
Stock-based compensation expense	$ 12,312	$ 15,317	$ 12,774
Research and development
Stock-based compensation expense
Stock-based compensation expense	6,693	7,821	6,186
General and administrative
Stock-based compensation expense
Stock-based compensation expense	$ 5,619	$ 7,496	$ 6,588

Stock-Based Compensation - Valuation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-based compensation expense
Expected dividend payable in foreseeable future	$ 0
Stock options
Black-Scholes option with following assumptions:
Expected stock price volatility, minimum (as a percent)	75.00%	70.00%	67.00%
Expected stock price volatility, maximum (as a percent)	77.00%	77.00%	69.00%
Expected option term	6 years	6 years	6 years
Risk-free interest rate, minimum (as a percent)	2.00%	1.40%	1.80%
Risk-free interest rate, maximum (as a percent)	2.30%	2.30%	2.20%
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%

Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue
Deferred revenue	$ 2,813				$ 3,749				$ 2,813	$ 3,749
Revenue.	$ 3,456	$ 3,924	$ 3,829	$ 1,534	$ 1,874	$ 2,220	$ 1,389	$ 1,303	12,743	6,786	$ 5,480
Rockefeller
Revenue
Revenue.									2,200	2,700	3,400
Bristol-Myers Squibb Company
Revenue
Estimated performance period (in years)												5 years
Deferred revenue												$ 5,000
Reimbursement of external costs (as percent)												50.00%
Revenue.									2,800	$ 2,100	$ 1,300
International AIDS Vaccine Initiative
Revenue
Revenue.									4,900
Frontier Biotechnologies Inc
Revenue
Revenue.									$ 1,700

Collaboration Agreements (Details) - USD ($) $ in Millions	12 Months Ended
Collaboration Agreements (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Collaborative Agreements
License fee expense	$ 0.7	$ 1.6	$ 0.9
Medarex
Collaborative Agreements
Period from the first commercial sale of licensed product for royalty payment	10 years
Rockefeller
Collaborative Agreements
Potential milestone payment	$ 3.8
Southampton
Collaborative Agreements
Potential milestone payment	1.0
Amgen
Collaborative Agreements
Potential milestone payment	0.9
Seattle Genetics \| Glembatumumab Vedotin
Collaborative Agreements
Potential milestone payment	5.0
Seattle Genetics \| CDX-014
Collaborative Agreements
Potential milestone payment	8.5
Yale
Collaborative Agreements
Potential milestone payment	3.0
MedImmune \| Obtaining specified regulatory and development
Collaborative Agreements
Potential milestone payment	45.0
MedImmune \| Specified annual net sales thresholds are met
Collaborative Agreements
Potential milestone payment	$ 125.0

Income Taxes - Benefit (Provision) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Benefit (Provision):
Federal	$ 57,547	$ 45,518	$ 46,598
State	(2,479)	7,268	10,642
Foreign	2,448	1,124
Income Tax Rate Change	(99,528)
Expiration of Net Operating Losses and Research & Development Tax Credits			(155)
Income tax benefit (provision) before valuation allowance	(42,012)	53,910	57,085
Deferred tax valuation allowance	66,294	$ (53,910)	$ (57,085)
Income Tax Benefit (Provision)	$ 24,282

Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation between the amount of reported income tax and the amount computed using U.S. Statutory rate
Pre-tax loss	$ (117,313)	$ (128,530)	$ (127,197)
Loss at Statutory Rates	(39,887)	(43,700)	(43,247)
Difference in Foreign Tax Rates	326	150
Research and Development Credits	(2,847)	(5,203)	(4,935)
State Taxes	(6,283)	(7,268)	(10,642)
Income Tax Rate Change	99,528
Other	(321)	2,111	1,584
Recognition of APIC NOLs	(5,729)
Impact of Pass-through Entities	(2,775)
Expiration of Net Operating Losses and Research & Development Tax Credits			155
Change in Valuation Allowance	(66,294)	$ 53,910	$ 57,085
Income Tax (Benefit) Provision	$ (24,282)

Income Taxes - Deferred Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 22, 2017	Dec. 31, 2016
Gross Deferred Tax Assets
Net Operating Loss Carryforwards		$ 146,228		$ 174,555
Foreign Net Operating Loss Carryforwards		3,572		1,124
Tax Credit Carryforwards		36,458		32,306
Deferred Research and Development Expenses		79,272		109,520
Stock-based Compensation		10,718		12,362
Fixed Assets		1,305		1,526
Deferred Revenue		686		1,418
Accrued Expenses and Other		316		894
Gross Deferred Tax Assets		278,555		333,705
Gross Deferred Tax Liabilities
Other Acquired Intangibles		(1,792)		(2,868)
IPR&D Intangibles		(15,992)		(28,054)
Total Deferred Tax Assets and Liabilities		260,771		302,783
Valuation Allowance		(264,543)		(330,837)
Net Deferred Tax Liability		(3,772)		$ (28,054)
Principal components of the deferred tax assets and liabilities
Increase in deferred tax and valuation allowance		$ 17,700
U.S. federal corporate income tax rate (as a percent)		35.00%
Change in tax rate, deferred tax liability benefit		$ 6,900
Additional income tax benefit leading to tax liabilities		12,200
Revaluation of deferred tax asset		99,500
Income tax benefit		$ 5,200
Forecast
Principal components of the deferred tax assets and liabilities
U.S. federal corporate income tax rate (as a percent)	21.00%
Maximum
Principal components of the deferred tax assets and liabilities
U.S. federal corporate income tax net operating losses (as a percent)			80.00%

Income Taxes - Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards
Foreign pre-tax loss	$ 8.2	$ 3.7
Federal
Operating Loss Carryforwards
Net operating loss carryforwards	561.8
Federal \| R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	29.0
State
Operating Loss Carryforwards
Net operating loss carryforwards	435.9
State \| R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	$ 9.5

Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Obligations for base rent and CAM costs under facility and other non-cancelable operating leases
2018	$ 4,591
2019	4,472
2020	2,498
Total minimum lease payments	11,561
Total rent and CAM expense	$ 4,100	$ 4,800	$ 2,900

Retirement Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
Retirement Savings Plan (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Savings Plan
Maximum contribution by participants (as a percent)	60.00%
Employer matching contributions (as a percent)	50.00%
Maximum percentage of employees' gross pay subject to employer matching contributions	4.00%
Benefit expense for the 401(k) Plan	$ 0.5	$ 0.4	$ 0.4

Kolltan Acquisition (Details) - Kolltan $ in Millions	Nov. 29, 2016 USD ($) shares
Kolltan Acquisition
Shares issued as part of consideration (in shares) \| shares	18,257,996
Specified development, regulatory approvals or sales-based milestones
Kolltan Acquisition
Milestone payments \| $	$ 172.5

Kolltan Acquisition - Purchase Price (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Nov. 29, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2017
Acquisition-date fair value of consideration transferred
Fair value of contingent consideration		$ 44,200	$ 44,200	$ 43,400
Kolltan transaction expenses paid in cash by the Company		$ 700	$ 700
Kolltan
Kolltan Acquisition
Price of common stock (in dollars per share)	$ 4.02
Acquisition-date fair value of consideration transferred
Fair value of common stock issued for upfront payment	$ 73,397
Fair value of contingent consideration	44,200
Kolltan transaction expenses paid in cash by the Company	3,768
Total consideration transferred	$ 121,365

Kolltan Acquisition - Allocations of Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Nov. 29, 2016
Kolltan Acquisition
Estimated development costs included in expected future net cash flows	$ 132,000
Goodwill expected to be deductible for income tax purposes			$ 0
Summary of fair values of assets acquired and liabilities assumed
Goodwill	$ 90,976	$ 90,976
Kolltan
Summary of fair values of assets acquired and liabilities assumed
Cash and cash equivalents			8,160
Other current and long-term assets			799
Property and equipment, net			2,072
In-process research and development (IPR&D)			61,690
Goodwill			82,011
Deferred tax liabilities, net			(23,393)
Other assumed liabilities			(9,974)
Total			121,365
Kolltan \| Anti-KIT Program
Summary of fair values of assets acquired and liabilities assumed
In-process research and development (IPR&D)			40,000
Kolltan \| CDX-3379
Summary of fair values of assets acquired and liabilities assumed
In-process research and development (IPR&D)			3,500
Kolltan \| TAM programs
Summary of fair values of assets acquired and liabilities assumed
In-process research and development (IPR&D)			$ 18,000

Kolltan Acquisition - Acquisition Related Expenses, Including Severance (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Nov. 29, 2016	Dec. 31, 2016	Dec. 31, 2016
Acquisition related expenses, including severance
Acquisition-related expenses		$ 700	$ 700
Kolltan
Acquisition related expenses, including severance
Acquisition-related expenses	$ 3,768
Severance expense		$ 3,100
Kolltan \| General and administrative
Acquisition related expenses, including severance
Severance expense			2,400
Kolltan \| Research and development
Acquisition related expenses, including severance
Severance expense			$ 700

Kolltan Acquisition - Pro Forma (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended								12 Months Ended
	Nov. 29, 2016	Dec. 31, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Kolltan Acquisition
Transaction expense		$ 700										$ 700
Revenue.			$ 3,456	$ 3,924	$ 3,829	$ 1,534	$ 1,874	$ 2,220	$ 1,389	$ 1,303	$ 12,743	6,786	$ 5,480
Kolltan
Kolltan Acquisition
Severance expense		3,100
Transaction expense	$ 3,768
Revenue.		$ 0
Pro Forma Financial Information
Revenue												6,786	5,480
Net loss												$ (146,905)	$ (157,690)
Basic and Diluted Net Loss Per Common Share												$ (1.24)	$ (1.37)

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Data (Unaudited)
Total revenue	$ 3,456	$ 3,924	$ 3,829	$ 1,534	$ 1,874	$ 2,220	$ 1,389	$ 1,303	$ 12,743	$ 6,786	$ 5,480
Net loss	$ (3,841)	$ (26,363)	$ (28,566)	$ (34,261)	$ (32,307)	$ (29,598)	$ (31,952)	$ (34,673)	$ (93,031)	$ (128,530)	$ (127,197)
Basic and diluted net loss per common share (in dollars per share)	$ (0.03)	$ (0.20)	$ (0.23)	$ (0.28)	$ (0.30)	$ (0.29)	$ (0.32)	$ (0.35)	$ (0.72)	$ (1.27)	$ (1.31)