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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	Apr. 30, 2020
Document and Entity Information
Document Type	10-Q
Document Period End Date	Mar. 31, 2020
Entity Registrant Name	Celldex Therapeutics, Inc.
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		18,938,085
Entity Central Index Key	0000744218
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and Cash Equivalents	$ 22,724	$ 11,232
Marketable Securities	30,998	53,151
Accounts and Other Receivables	1,108	1,015
Prepaid and Other Current Assets	1,088	1,300
Total Current Assets	55,918	66,698
Property and Equipment, Net	4,116	4,031
Operating Lease Right-of-Use Assets, Net	3,739	3,473
Intangible Assets, Net	48,690	48,690
Other Assets	41	41
Total Assets	112,504	122,933
Current Liabilities:
Accounts Payable	1,609	1,174
Accrued Expenses	5,648	6,499
Current Portion of Operating Lease Liabilities	1,682	1,944
Current Portion of Long-Term Liabilities	1,993	2,026
Total Current Liabilities	10,932	11,643
Long-Term Portion of Operating Lease Liabilities	2,106	1,713
Other Long-Term Liabilities	15,763	15,551
Total Liabilities	28,801	28,907
Commitments and Contingent Liabilities (Note 14)
Stockholders' Equity:
Convertible Preferred Stock, $.01 Par Value; 3,000,000 Shares Authorized; No Shares Issued and Outstanding at March 31, 2020 and December 31, 2019, Respectively
Common Stock, $.001 Par Value; 297,000,000 Shares Authorized; 17,730,802 and 16,972,077 Shares Issued and Outstanding at March 31, 2020 and December 31, 2019, Respectively	18	17
Additional Paid-In Capital	1,107,029	1,104,706
Accumulated Other Comprehensive Income	2,597	2,619
Accumulated Deficit	(1,025,941)	(1,013,316)
Total Stockholders' Equity	83,703	94,026
Total Liabilities and Stockholders' Equity	$ 112,504	$ 122,933

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
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	17,730,802	16,972,077
Common Stock, Shares Outstanding	17,730,802	16,972,077

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
REVENUES:
Total Revenues	$ 2,728	$ 1,425
OPERATING EXPENSES:
Research and Development	11,695	11,151
General and Administrative	3,666	4,896
Other Asset Impairment		1,800
Gain on Fair Value Remeasurement of Contingent Consideration	234	1,519
Total Operating Expenses	15,595	19,366
Operating Loss	(12,867)	(17,941)
Investment and Other Income, Net	242	702
Net Loss	$ (12,625)	$ (17,239)
Basic and Diluted Net Loss Per Common Share	$ (0.73)	$ (1.40)
Shares Used in Calculating Basic and Diluted Net Loss per Share	17,406	12,297
COMPREHENSIVE LOSS:
Net Loss	$ (12,625)	$ (17,239)
Other Comprehensive Income (Loss):
Unrealized Gain on Marketable Securities	(22)	19
Comprehensive Loss	(12,647)	(17,220)
Product Development and Licensing Agreements
REVENUES:
Total Revenues	2,286	129
Contracts and Grants
REVENUES:
Total Revenues	$ 442	$ 1,296

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash Flows From Operating Activities:
Net Loss	$ (12,625)	$ (17,239)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	1,165	1,352
Amortization and Premium of Marketable Securities, Net	(63)	(345)
Loss on Sale or Disposal of Assets		25
Other Asset Impairment		1,800
Gain on Fair Value Remeasurement of Contingent Consideration	234	1,519
Stock-Based Compensation Expense	687	1,693
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	(93)	855
Prepaid and Other Current Assets	206	299
Accounts Payable and Accrued Expenses	(853)	(1,455)
Other Liabilities	(768)	(1,737)
Net Cash Used in Operating Activities	(12,110)	(13,233)
Cash Flows From Investing Activities:
Sales and Maturities of Marketable Securities	22,200	37,886
Purchases of Marketable Securities		(21,404)
Acquisition of Property and Equipment	(235)	(186)
Net Cash Provided by Investing Activities	21,965	16,296
Cash Flows From Financing Activities:
Net Proceeds from Stock Issuances	1,613	4,151
Proceeds from Issuance of Stock from Employee Benefit Plans	24	9
Net Cash Provided by Financing Activities	1,637	4,160
Net Decrease in Cash and Cash Equivalents	11,492	7,223
Cash and Cash Equivalents at Beginning of Period	11,232	11,232
Cash and Cash Equivalents at End of Period	22,724	31,533
Non-cash Investing Activities
Accrued construction in progress	$ 462	$ 65

Basis of Presentation	3 Months Ended
Basis of Presentation	Mar. 31, 2020
Basis of Presentation
Basis of Presentation	(1) Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared by Celldex Therapeutics, Inc. (the “Company” or “Celldex”) in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and reflect the operations of the Company and its wholly-owned subsidiary. All intercompany balances and transactions have been eliminated in consolidation. These interim financial statements do not include all the information and footnotes required by U.S. GAAP for annual financial statements and should be read in conjunction with the audited financial statements for the year ended December 31, 2019, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 26, 2020. In the opinion of management, the interim financial statements reflect all normal recurring adjustments necessary to fairly state the Company’s financial position and results of operations for the interim periods presented. The year-end condensed balance sheet data presented for comparative purposes was derived from audited financial statements but does not include all disclosures required by U.S. GAAP. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for any future interim period or the fiscal year ending December 31, 2020. Under U.S. GAAP, the Company has the responsibility to evaluate whether conditions and/or events raise substantial doubt about its ability to meet its future financial obligations as they become due within one year after the date that the financial statements are issued. This evaluation shall initially not take into consideration the potential mitigating effects of plans that have not been fully implemented as of the date the financial statements are issued. The Company's financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. At March 31, 2020, the Company had cash, cash equivalents and marketable securities of $53.7 million. The Company has had recurring losses and incurred a loss of $12.6 million for the three months ended March 31, 2020. Net cash used in operations for the three months ended March 31, 2020 was $12.1 million. As of May 6, 2020, the date of issuance of the consolidated financial statements, the Company expects that its cash, cash equivalents and marketable securities of $53.7 million as of March 31, 2020 will be sufficient to fund its operating expenses and capital expenditure requirements into the second quarter of 2021. The future viability of the Company beyond that point is dependent on the Company’s ability to raise additional capital to finance its operations. The Company has generated no product revenue to date and cannot predict when and if it will generate product revenue. The Company has had recurring losses and anticipate operating losses to continue for the foreseeable future due to, among other things, costs related to research, development of product candidates, conducting preclinical studies and clinical trials, facilities and general and administrative expenses. These conditions raise substantial doubt about the Company’s ability to continue as a going concern for one year after the date that the financial statements are issued. During the next twelve months and beyond, the Company will take further steps to raise additional capital to meet its liquidity needs including, 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. Although the Company has been successful in raising capital in the past, 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 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. The financial statements do not include any adjustments that might result from the outcome of this uncertainty. In December 2019, a novel strain of coronavirus, now referred to as COVID-19, surfaced in Wuhan, China. The virus continues to spread globally, has been declared a pandemic by the World Health Organization and has spread to over 200 countries, including the United States. The impact of this pandemic has been and will likely continue to be extensive in many aspects of society, which has resulted in and will likely continue to result in significant disruptions to the global economy, as well as businesses and capital markets around the world. COVID-19 has had a more severe impact in New Jersey, Massachusetts and Connecticut, where the Company has office, research and manufacturing facilities, than in other parts of the United States. In an effort to halt the outbreak of COVID-19, various states, including New Jersey, Massachusetts and Connecticut, have placed significant restrictions on travel and many businesses have announced extended closures which could adversely impact our operations. To date, the Company has not experienced significant delays or disruptions in planned and ongoing preclinical and clinical trials, manufacturing or shipping. Potential impacts to our business include delays in planned and ongoing preclinical and clinical trials including enrollment of patients, disruptions in time and resources provided by independent clinical investigators, contract research organizations, other third-party service providers, temporary closures of our facilities, disruptions or restrictions on our employees' ability to travel, and delays in manufacturing and/or shipments to and from third party suppliers and contract manufacturers for APIs and drug product. Any prolonged negative impacts to our business could materially impact our operating results and could lead to impairments of our Intangible (IPR&D) assets which amounted to $48.7 million at March 31, 2020.

Significant Accounting Policies	3 Months Ended
Significant Accounting Policies	Mar. 31, 2020
Significant Accounting Policies
Significant Accounting Policies	(2) Significant Accounting Policies The significant accounting policies used in preparation of these condensed consolidated financial statements on Form 10-Q for the three months ended March 31, 2020 are consistent with those discussed in Note 2 to the financial statements in our Annual Report on Form 10-K for the year ended December 31, 2019, except as it relates to the adoption of new accounting standards during the first three months of 2020 as discussed below. Newly Adopted Accounting Pronouncements On January 1, 2020, the Company adopted a new accounting standard that modifies certain disclosure requirements for fair value measurements. For instance, the Company is required to disclose weighted average information for significant unobservable inputs for all Level 3 fair value measurements. The adoption of this new guidance did not have a material impact on the Company's consolidated financial statements and related disclosures. Refer to Note 3 for the disclosures related to the Company's level 3 fair value measurements. On January 1, 2020, the Company adopted a new accounting standard that clarifies the interaction between the accounting guidance for collaborative arrangements and revenue from contracts with customers. The amendments clarify that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606, when the collaborative arrangement participant is a customer in the context of a unit of account. The adoption of this standard did not have a material impact on our consolidated financial statements, as we have no arrangements within the scope of ASC 808. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the 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 June 2016, the FASB issued guidance on the Measurement of Credit Losses on Financial Instruments. The guidance requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with unrealized losses, the standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. This standard will be effective for the Company on January 1, 2023. We are currently evaluating the potential impact that this standard may have on the Company’s consolidated financial statements and related disclosures.

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

Fair Value Measurements

Fair Value Measurements

(3) Fair Value Measurements

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


	As of
	March 31, 2020		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	15,396		—	$	15,396		—
Marketable securities		30,998		—		30,998		—
	$	46,394		—	$	46,394		—
Liabilities:
Kolltan acquisition contingent consideration	$	12,719		—		—	$	12,719
	$	12,719		—		—	$	12,719


	As of
	December 31, 2019		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	4,024		—	$	4,024		—
Marketable securities		53,151		—		53,151		—
	$	57,175		—	$	57,175		—
Liabilities:
Kolltan acquisition contingent consideration	$	12,485		—		—	$	12,485
	$	12,485		—		—	$	12,485

The Company’s financial assets consist mainly of money market funds, 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 three months ended March 31, 2020 (in thousands):


	Other Liabilities:
	Contingent
	Consideration
Balance at December 31, 2019	$	12,485
Fair value adjustments included in operating expenses		234
Balance at March 31, 2020	$	12,719

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, was primarily an income approach. 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. As of March 31, 2020, the weighted average discount rate used in calculating the fair value of contingent consideration was 16.5% (with a range of 16.3% to 18.9%) and the weighted average amount of time until the conditions of the milestone payments are met was 3 years.

During the three months ended March 31, 2020, the Company recorded a $0.2 million loss on fair value remeasurement of contingent consideration, respectively, primarily due to the passage of time. During the three months ended March 31, 2019, the Company recorded a $1.5 million loss on fair value remeasurement of contingent consideration, primarily due to changes in discount rates and the passage of time. The assumptions related to determining the fair 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 adjustment recorded in any given period.

The Company did not have any transfers in or out of Level 3 assets or liabilities during the three months ended March 31, 2020.

- 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

3 Months Ended

Mar. 31, 2020

Marketable Securities

Marketable Securities

(4) Marketable Securities

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


	Gross Unrealized
	Amortized						Fair
	Cost		Gains		Losses		Value
	(In thousands)
March 31, 2020
U.S. government and municipal obligations (maturing in one year or less)	$	10,538	$	16	$	—	$	10,554
Corporate debt securities (maturing in one year or less)		20,459		—		(15)		20,444
Total Marketable Securities	$	30,997	$	16	$	(15)	$	30,998

December 31,2019
U.S. government and municipal obligations (maturing in one year or less)	$	18,509	$	13	$	—	$	18,522
Corporate debt securities (maturing in one year or less)		34,619		13		(3)		34,629
Total Marketable Securities	$	53,128	$	26	$	(3)	$	53,151

The Company holds investment-grade marketable securities, and none were in a continuous unrealized loss position for more than twelve months as of March 31, 2020 and December 31, 2019. The unrealized losses are attributable to changes in interest rates and the Company does not believe any unrealized losses represent other-than-temporary impairments. Marketable securities include $0.2 million in accrued interest at March 31, 2020 and December 31, 2019.

Intangible Assets	3 Months Ended
Intangible Assets	Mar. 31, 2020
Intangible Assets
Intangible Assets	(5) Intangible Assets At March 31, 2020 and 2019, the Company recorded indefinite-lived intangible assets of $48.7 million. Indefinite-lived intangible assets consist of acquired in-process research and development (“IPR&D”) related to the development of CDX-3379, the anti-KIT program (including CDX-0159) and the TAM program. CDX-3379 is in Phase 2 development, CDX-0159 is in Phase 1 development, and the TAM program is in preclinical development. As of March 31, 2020, none of the Company’s IPR&D assets 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. 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.

Other Assets	3 Months Ended
Other Assets	Mar. 31, 2020
Other Assets
Other Assets	(6) Other Assets In 2016, the Company entered into a research and collaboration agreement with an undisclosed private company to access novel technologies and paid $3.5 million to support research activities and make an investment in the private company. The Company recorded $1.8 million to other assets related to this investment and $1.7 million was recorded to research and development expense over the term of the research activities. The stock of the private company does not have a readily determinable fair value, and therefore it is measured at cost less impairment, if any. Based on information received in April 2019, it was determined that there was a deterioration of the private company’s financial condition due to a working capital deficiency and an inability to secure additional funding as of March 31, 2019. Therefore, the Company concluded that the investment was impaired, and a non-cash impairment charge of $1.8 million was recorded during the first quarter of 2019.

Other Long-Term Liabilities

3 Months Ended

Mar. 31, 2020

Other Long-Term Liabilities

Other Long-Term Liabilities

(7) Other Long-Term Liabilities

Other long-term liabilities include the following:


	March 31, 2020		December 31, 2019
	(In thousands)
Net Deferred Tax Liabilities Related to IPR&D (Note 12)	$	3,007	$	3,007
Deferred Income From Sale of Tax Benefits		1,831		1,831
Contingent Milestones (Note 3)		12,719		12,485
Deferred Revenue (Note 11)		199		254
Total		17,756		17,577
Less Current Portion		(1,993)		(2,026)
Long-Term Portion	$	15,763	$	15,551

In November 2015, the Company received approval from the New Jersey Economic Development Authority and agreed to sell New Jersey tax benefits of $9.8 million to an independent third party for $9.2 million. 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. The Company recognized $0.0 million and $0.2 million in other income related to the sale of these tax benefits during the three months ended March 31, 2020 and 2019, respectively.

Stockholders' Equity

3 Months Ended

Mar. 31, 2020

Stockholders' Equity

Stockholders' Equity

(8) Stockholders’ Equity

In May 2016, the Company entered into a controlled equity offering sales agreement agreement (the “Cantor Agreement”) with Cantor Fitzgerald & Co. (“Cantor”) to allow the Company to issue and sell shares of its common stock from time to time through Cantor, acting as agent. In March 2020, the Company filed a prospectus supplement for the amount of shares that the Company is eligible to sell pursuant to the Cantor Agreement. Under the March 2020 prospectus supplement, the Company may offer and sell shares of common stock having an aggregate offering price of up to $18,000,000. During the three months ended March 31, 2020, the Company issued 0.7 million shares of common stock pursuant to the Cantor Agreement resulting in net proceeds of $1.6 million after deducting commission and offering expenses. At March 31, 2020, the Company had $17.9 million remaining in aggregate gross offering price available under the March 2020 prospectus supplement. In April 2020, the Company issued 1.2 million shares of its common stock resulting in net proceeds to the Company of $2.9 million.

The changes in Stockholders’ Equity during the three months ended March 31, 2020 and 2019 are summarized below:


						Accumulated
	Common	Common		Additional		Other				Total
	Stock	Stock Par		Paid-In		Comprehensive		Accumulated		Stockholders’
	Shares	Value		Capital		Income		Deficit		Equity
	(In thousands, except share amounts)
Consolidated Balance at December 31, 2019	16,972,077		17		1,104,706		2,619		(1,013,316)		94,026
Shares Issued under Stock Option and Employee Stock Purchase Plans	12,573		—		24		—		—		24
Shares Issued in Connection with Cantor Agreement	746,152		1		1,613		—		—		1,614
Share-Based Compensation	—		—		686		—		—		686
Unrealized Loss on Marketable Securities	—		—		—		(22)		—		(22)
Net Loss	—		—		—		—		(12,625)		(12,625)
Consolidated Balance at March 31, 2020	17,730,802	$	18	$	1,107,029	$	2,597	$	(1,025,941)	$	83,703

						Accumulated
	Common	Common		Additional		Other				Total
	Stock	Stock Par		Paid-In		Comprehensive		Accumulated		Stockholders’
	Shares	Value		Capital		Income		Deficit		Equity
	(In thousands, except share amounts)
Consolidated Balance at December 31, 2018	11,957,635		12		1,083,903		2,583		(962,438)		124,060
Shares Issued under Stock Option and Employee Stock Purchase Plans	3,507		—		9		—		—		9
Shares Issued in Connection with Cantor Agreement	883,569		1		4,150		—		—		4,151
Share-Based Compensation	—		—		1,693		—		—		1,693
Unrealized Loss on Marketable Securities	—		—		—		19		—		19
Net Loss	—		—		—		—		(17,239)		(17,239)
Consolidated Balance at March 31, 2019	12,844,711	$	13	$	1,089,755	$	2,602	$	(979,677)	$	112,693

Stock-Based Compensation

3 Months Ended

Mar. 31, 2020

Stock-Based Compensation

Stock-Based Compensation

(9) Stock-Based Compensation

A summary of stock option activity for the three months ended March 31, 2020 is as follows:


		Weighted		Weighted
		Average		Average
		Exercise		Remaining
		Price		Contractual
	Shares	Per Share		Term (In Years)
Options Outstanding at December 31, 2019	1,699,202	$	44.87	8.0
Granted	2,750	$	1.66
Exercised	—		—
Canceled	(43,811)	$	50.59
Options Outstanding at March 31, 2020	1,658,141	$	44.65	7.8
Options Vested and Expected to Vest at March 31, 2020	1,585,639	$	46.50	7.8
Options Exercisable at March 31, 2020	576,042	$	118.98	5.6
Shares Available for Grant Under the 2008 Plan	465,324

The weighted average grant-date fair value of stock options granted during the three month period ended March 31, 2020 was $1.23. Stock-based compensation expense for the three months ended March 31, 2020 and 2019 was recorded as follows:


	Three months ended March 31,
	2020		2019
	(In thousands)
Research and development	$	310	$	756
General and administrative		377		937
Total stock-based compensation expense	$	687	$	1,693

The fair values of employee and director stock options granted during the three months ended March 31, 2020 and 2019 were valued using the Black-Scholes option pricing model with the following assumptions:


	Three months ended March 31,
	2020		2019
Expected stock price volatility	91	%	91	%
Expected option term	6.0	Years	6.0	Years
Risk-free interest rate	0.6	%	2.5	%
Expected dividend yield	None		None

Accumulated Other Comprehensive Income

3 Months Ended

Mar. 31, 2020

Accumulated Other Comprehensive Income

Accumulated Other Comprehensive Income

(10) Accumulated Other Comprehensive Income

The changes in accumulated other comprehensive income, which is reported as a component of stockholders’ equity, for the three months ended March 31, 2020 are summarized below:


	Unrealized
	Gain/(Loss) on
	Marketable		Foreign
	Securities		Currency Items		Total
	(In thousands)
Balance at December 31, 2019	$	23	$	2,596	$	2,619
Other comprehensive loss		(22)		—		(22)
Balance at March 31, 2020	$	1	$	2,596	$	2,597

No amounts were reclassified out of accumulated other comprehensive income during the three months ended March 31, 2020.

Revenue	3 Months Ended
Revenue	Mar. 31, 2020
Revenue
Revenue	(11) Revenue Product Development and Licensing Revenue The Company entered into an agreement with Rockefeller University in September 2013, as amended, (the “Rockefeller Agreement”) pursuant to which the Company performs manufacturing and development services for Rockefeller University for their portfolio of antibodies against HIV. This portfolio was licensed to Gilead Sciences in January 2020 from Rockefeller University (“Rockefeller Transaction”). Pursuant to the Rockefeller Agreement, the Company received an upfront payment of $1.8 million as a result of the Rockefeller Transaction which was recorded to revenue during the three months ended March 31, 2020. The Company is eligible to receive additional payments from Rockefeller University if this portfolio progresses through clinical and commercial development. Contract and Grants Revenue The Company has entered into the Rockefeller Agreement and an agreement with Duke University pursuant to which the Company performs manufacturing and research and development services on a time-and-materials basis. The Company recognized $0.4 million and $1.2 million in revenue for labor hours and direct costs incurred under these agreements during the three months ended March 31, 2020 and 2019, respectively. Contract Assets and Liabilities At December 31, 2019 and March 31, 2020, the Company’s right to consideration under all contracts was considered unconditional, and as such, there were no recorded contract assets. At December 31, 2019 and March 31, 2020, the Company had $0.3 million and $0.2 million in contract liabilities recorded, respectively. Revenue recognized from contract liabilities as of December 31, 2019 during the three months ended March 31, 2020 was $0.1 million.

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2020
Income Taxes
Income Taxes	(12) Income Taxes 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 as of March 31, 2020 and December 31, 2019. The net deferred tax liability of $3.0 million at March 31, 2020 and December 31, 2019 relates to the temporary differences associated with the IPR&D intangible assets acquired in previous business combinations and is not deductible for tax purposes. Massachusetts, New Jersey, New York and Connecticut 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.

Net Loss Per Share

3 Months Ended

Mar. 31, 2020

Net Loss Per Share

Net Loss Per Share

(13) 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. In periods in which the Company reports a net loss, there is no difference between basic and diluted net loss per share because dilutive shares of common stock are not assumed to have been issued as their effect is anti-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:


	Three Months Ended March 31,
	2020	2019
Stock Options	1,658,141	836,104
Restricted Stock	1,110	3,552
	1,659,251	839,656

Kolltan Acquisition	3 Months Ended
Kolltan Acquisition	Mar. 31, 2020
Kolltan Acquisition
Kolltan Acquisition	(14) 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 1,217,200 shares of the Company’s common stock plus contingent consideration in the form of development, regulatory approval and sales-based milestones (“Kolltan Milestones”) of up to $172.5 million. The Kolltan Milestone payments, if any, may be made, at Celldex’s sole election, in cash, in shares of Celldex’s common stock or a combination of both, subject to provisions of the Merger Agreement. Certain Kolltan Milestones have been abandoned consistent with the provisions of the Merger Agreement and, because of this, as of March 31, 2020, the Company believes that the adjusted amount we may be required to pay for future consideration is up to $127.5 million contingent upon the achievement of the Kolltan Milestones. In October 2019, the Company received a letter from the representative of Kolltan’s former stockholders notifying the Company that it objected to the Company’s abandonment of certain Kolltan Milestones relating to development, regulatory approval and sales-based milestones. The Company disagrees with their objection and believes their objection to be without merit. The Company is discussing with the representative of Kolltan’s former stockholders potential amendments to the Merger Agreement with respect to the Kolltan Milestones. There can be no assurances that an amendment to the Merger Agreement will be completed on terms acceptable to the Company or at all. At this time, the Company is unable to reasonably assess the ultimate outcome of the Company’s disagreement with the representative of Kolltan’s former stockholders over its objection to the Company’s abandonment of certain Kolltan Milestones or determine an estimate of potential losses, if any.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2020
Significant Accounting Policies
Newly-Adopted Accounting Pronouncements	Newly Adopted Accounting Pronouncements On January 1, 2020, the Company adopted a new accounting standard that modifies certain disclosure requirements for fair value measurements. For instance, the Company is required to disclose weighted average information for significant unobservable inputs for all Level 3 fair value measurements. The adoption of this new guidance did not have a material impact on the Company's consolidated financial statements and related disclosures. Refer to Note 3 for the disclosures related to the Company's level 3 fair value measurements. On January 1, 2020, the Company adopted a new accounting standard that clarifies the interaction between the accounting guidance for collaborative arrangements and revenue from contracts with customers. The amendments clarify that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606, when the collaborative arrangement participant is a customer in the context of a unit of account. The adoption of this standard did not have a material impact on our consolidated financial statements, as we have no arrangements within the scope of ASC 808.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the 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 June 2016, the FASB issued guidance on the Measurement of Credit Losses on Financial Instruments. The guidance requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with unrealized losses, the standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. This standard will be effective for the Company on January 1, 2023. We are currently evaluating the potential impact that this standard may have on the Company’s consolidated financial statements and related disclosures.

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Measurements

Schedule of financial assets and liabilities subject to fair value measurements


	As of
	March 31, 2020		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	15,396		—	$	15,396		—
Marketable securities		30,998		—		30,998		—
	$	46,394		—	$	46,394		—
Liabilities:
Kolltan acquisition contingent consideration	$	12,719		—		—	$	12,719
	$	12,719		—		—	$	12,719


	As of
	December 31, 2019		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	4,024		—	$	4,024		—
Marketable securities		53,151		—		53,151		—
	$	57,175		—	$	57,175		—
Liabilities:
Kolltan acquisition contingent consideration	$	12,485		—		—	$	12,485
	$	12,485		—		—	$	12,485

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


	Other Liabilities:
	Contingent
	Consideration
Balance at December 31, 2019	$	12,485
Fair value adjustments included in operating expenses		234
Balance at March 31, 2020	$	12,719

Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2020

Marketable Securities

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


	Gross Unrealized
	Amortized						Fair
	Cost		Gains		Losses		Value
	(In thousands)
March 31, 2020
U.S. government and municipal obligations (maturing in one year or less)	$	10,538	$	16	$	—	$	10,554
Corporate debt securities (maturing in one year or less)		20,459		—		(15)		20,444
Total Marketable Securities	$	30,997	$	16	$	(15)	$	30,998

December 31,2019
U.S. government and municipal obligations (maturing in one year or less)	$	18,509	$	13	$	—	$	18,522
Corporate debt securities (maturing in one year or less)		34,619		13		(3)		34,629
Total Marketable Securities	$	53,128	$	26	$	(3)	$	53,151

Other Long-Term Liabilities (Tables)

3 Months Ended

Mar. 31, 2020

Other Long-Term Liabilities

Schedule of other long-term liabilities


	March 31, 2020		December 31, 2019
	(In thousands)
Net Deferred Tax Liabilities Related to IPR&D (Note 12)	$	3,007	$	3,007
Deferred Income From Sale of Tax Benefits		1,831		1,831
Contingent Milestones (Note 3)		12,719		12,485
Deferred Revenue (Note 11)		199		254
Total		17,756		17,577
Less Current Portion		(1,993)		(2,026)
Long-Term Portion	$	15,763	$	15,551

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2020

Stockholders' Equity

Schedule of Shareholder's equity


						Accumulated
	Common	Common		Additional		Other				Total
	Stock	Stock Par		Paid-In		Comprehensive		Accumulated		Stockholders’
	Shares	Value		Capital		Income		Deficit		Equity
	(In thousands, except share amounts)
Consolidated Balance at December 31, 2019	16,972,077		17		1,104,706		2,619		(1,013,316)		94,026
Shares Issued under Stock Option and Employee Stock Purchase Plans	12,573		—		24		—		—		24
Shares Issued in Connection with Cantor Agreement	746,152		1		1,613		—		—		1,614
Share-Based Compensation	—		—		686		—		—		686
Unrealized Loss on Marketable Securities	—		—		—		(22)		—		(22)
Net Loss	—		—		—		—		(12,625)		(12,625)
Consolidated Balance at March 31, 2020	17,730,802	$	18	$	1,107,029	$	2,597	$	(1,025,941)	$	83,703

						Accumulated
	Common	Common		Additional		Other				Total
	Stock	Stock Par		Paid-In		Comprehensive		Accumulated		Stockholders’
	Shares	Value		Capital		Income		Deficit		Equity
	(In thousands, except share amounts)
Consolidated Balance at December 31, 2018	11,957,635		12		1,083,903		2,583		(962,438)		124,060
Shares Issued under Stock Option and Employee Stock Purchase Plans	3,507		—		9		—		—		9
Shares Issued in Connection with Cantor Agreement	883,569		1		4,150		—		—		4,151
Share-Based Compensation	—		—		1,693		—		—		1,693
Unrealized Loss on Marketable Securities	—		—		—		19		—		19
Net Loss	—		—		—		—		(17,239)		(17,239)
Consolidated Balance at March 31, 2019	12,844,711	$	13	$	1,089,755	$	2,602	$	(979,677)	$	112,693

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Stock-Based Compensation

Summary of stock option activity


		Weighted		Weighted
		Average		Average
		Exercise		Remaining
		Price		Contractual
	Shares	Per Share		Term (In Years)
Options Outstanding at December 31, 2019	1,699,202	$	44.87	8.0
Granted	2,750	$	1.66
Exercised	—		—
Canceled	(43,811)	$	50.59
Options Outstanding at March 31, 2020	1,658,141	$	44.65	7.8
Options Vested and Expected to Vest at March 31, 2020	1,585,639	$	46.50	7.8
Options Exercisable at March 31, 2020	576,042	$	118.98	5.6
Shares Available for Grant Under the 2008 Plan	465,324

Schedule of stock-based compensation expense


	Three months ended March 31,
	2020		2019
	(In thousands)
Research and development	$	310	$	756
General and administrative		377		937
Total stock-based compensation expense	$	687	$	1,693

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


	Three months ended March 31,
	2020		2019
Expected stock price volatility	91	%	91	%
Expected option term	6.0	Years	6.0	Years
Risk-free interest rate	0.6	%	2.5	%
Expected dividend yield	None		None

Accumulated Other Comprehensive Income (Tables)

3 Months Ended

Mar. 31, 2020

Accumulated Other Comprehensive Income

Summary of changes in accumulated other comprehensive income


	Unrealized
	Gain/(Loss) on
	Marketable		Foreign
	Securities		Currency Items		Total
	(In thousands)
Balance at December 31, 2019	$	23	$	2,596	$	2,619
Other comprehensive loss		(22)		—		(22)
Balance at March 31, 2020	$	1	$	2,596	$	2,597

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2020

Net Loss Per Share

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


	Three Months Ended March 31,
	2020	2019
Stock Options	1,658,141	836,104
Restricted Stock	1,110	3,552
	1,659,251	839,656

Basis of Presentation (Details) - USD ($) $ in Thousands	3 Months Ended
Basis of Presentation (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 53,700
Net Loss	(12,625)	$ (17,239)
Net cash used in operations	12,110	13,233
Indefinite-lived intangible assets	$ 48,700	$ 48,700

Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Liabilities:
Kolltan acquisition contingent consideration	$ 12,719	$ 12,485
Fair value \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	12,719	12,485
Fair Value Measurements. \| Level 2
Assets:
Money market funds and cash equivalents	15,396	4,024
Marketable securities	30,998	53,151
Total financial assets at fair value	46,394	57,175
Fair Value Measurements. \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	12,719	12,485
Total financial liabilities at fair value	12,719	12,485
Fair Value Measurements. \| Fair value
Assets:
Money market funds and cash equivalents	15,396	4,024
Marketable securities	30,998	53,151
Total financial assets at fair value	46,394	57,175
Liabilities:
Kolltan acquisition contingent consideration	12,719	12,485
Total financial liabilities at fair value	$ 12,719	$ 12,485

Fair Value Measurements - Contingent Consideration Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Contingent consideration liabilities measured at fair value
Balance at beginning of period	$ 12,485
Balance at end of period	12,719
Fair value \| Level 3
Contingent consideration liabilities measured at fair value
Balance at beginning of period	12,485
Fair value adjustments included in operating expenses	234
Balance at end of period	$ 12,719

Fair Value Measurements - Additional information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) Y	Mar. 31, 2019 USD ($)
Fair value measurements
Gain on Fair Value Remeasurement of Contingent Consideration	$ 234	$ 1,519
Discount rate \| Weighted average
Fair value measurements
Measurement input	0.165
Discount rate \| Minimum
Fair value measurements
Measurement input	0.163
Discount rate \| Maximum
Fair value measurements
Measurement input	0.189
Time until the conditions of the milestone payments are met
Fair value measurements
Measurement input \| Y	3
Fair value
Fair value measurements
Asset transfer out of level 3	$ 0
Asset transfer into level 3	0
Liabilities transfers out of level 3	0
Liabilities transfers into level 3	$ 0

Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Amortized Cost	$ 30,997	$ 53,128
Gross Unrealized Gains
Gross Unrealized Gains	16	26
Gross Unrealized Losses
Gross Unrealized Losses	(15)	(3)
Fair Value
Fair Value	30,998	53,151
U.S. government and municipal obligations
Amortized Cost
Maturing in one year or less	10,538	18,509
Gross Unrealized Gains
Maturing in one year or less	16	13
Fair Value
Maturing in one year or less	10,554	18,522
Corporate debt securities
Amortized Cost
Maturing in one year or less	20,459	34,619
Gross Unrealized Gains
Maturing in one year or less		13
Gross Unrealized Losses
Maturing in one year or less	(15)	(3)
Fair Value
Maturing in one year or less	$ 20,444	$ 34,629

Marketable Securities - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Marketable Securities
Number of investment-grade securities in unrealized loss position over 12 months	$ 0	$ 0
Accrued interest	$ 200	$ 200

Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Intangible Assets
Indefinite-lived intangible assets	$ 48.7	$ 48.7

Other Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Other Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2016
Other Assets
Cash paid to support research activities and investment in private company		$ 3.5
Other assets related to investment in undisclosed private company		1.8
Other assets related to research and development expense		$ 1.7
Non-cash impairment charge on investments	$ 1.8

Other Long-Term Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Other Long-Term Liabilities
Net Deferred Tax Liabilities Related to IPR&D (Note 12)	$ 3,007	$ 3,007
Deferred Income From Sale of Tax Benefits	1,831	1,831
Contingent Milestones (Note 3)	12,719	12,485
Deferred Revenue	199	254
Total	17,756	17,577
Less Current Portion	(1,993)	(2,026)
Long-Term Portion	$ 15,763	$ 15,551

Other Long-Term Liabilities- New Jersey tax benefits (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Nov. 30, 2015	Mar. 31, 2020	Mar. 31, 2019
Investment and other income		$ 242	$ 702
New Jersey tax benefits
Amount of tax benefit	$ 9,800
Proceeds from sale of tax credits	$ 9,200
Base of operations requirement (in years)	5 years
Investment and other income		$ 0	$ 200

Stockholders' Equity (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
Stockholders' Equity (Details) - USD ($) $ in Thousands	Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 2019
Common Stock
Period Start Balance	$ 83,703	$ 94,026	$ 124,060
Balance (in shares)	17,730,802	16,972,077
Shares Issued under Stock Option and Employee Stock Purchase Plans		$ 24	9
Maximum aggregate offering price of securities available for sale		18,000
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition		686	1,693
Shares Issued In Connection With Cantor Agreement		1,614	4,151
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		(22)	19
Net Income (Loss) Available to Common Stockholders, Basic		(12,625)	(17,239)
Period End Balance		$ 83,703	112,693
Balance (in shares)		17,730,802
Net proceeds from sale of common stock		$ 1,613	4,151
Common Stock
Common Stock
Period Start Balance	$ 18	$ 17	$ 12
Balance (in shares)	17,730,802	16,972,077	11,957,635
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)		12,573	3,507
Shares Issued In Connection With Cantor Agreement		$ 1	$ 1
Shares Issued in Connection with Cantor Agreement (in shares)		746,152	883,569
Period End Balance		$ 18	$ 13
Balance (in shares)		17,730,802	12,844,711
Aggregate gross offering price available		$ 17,900
Net proceeds from sale of common stock		1,600
Common Stock \| Subsequent Event
Common Stock
Common stock issued (in shares)	1,200,000
Net proceeds from sale of common stock	$ 2,900
Additional Paid-In Capital
Common Stock
Period Start Balance	1,107,029	1,104,706	$ 1,083,903
Shares Issued under Stock Option and Employee Stock Purchase Plans		24	9
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition		686	1,693
Shares Issued In Connection With Cantor Agreement		1,613	4,150
Period End Balance		1,107,029	1,089,755
Accumulated Other Comprehensive Income.
Common Stock
Period Start Balance	2,597	2,619	2,583
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		(22)	19
Period End Balance		2,597	2,602
Accumulated Deficit
Common Stock
Period Start Balance	$ (1,025,941)	(1,013,316)	(962,438)
Net Income (Loss) Available to Common Stockholders, Basic		(12,625)	(17,239)
Period End Balance		$ (1,025,941)	$ (979,677)

Stock-Based Compensation - Stock Option Activity (Details) - Stock options - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Shares
Options Outstanding at beginning of the period (in shares)	1,699,202
Granted (in shares)	2,750
Canceled (in shares)	(43,811)
Options Outstanding at the end of the period (in shares)	1,658,141	1,699,202
Options Vested and Expected to Vest at the end of the period (in shares)	1,585,639
Options Exercisable at the end of the period (in shares)	576,042
Shares Available for Grant Under the 2008 Plan	465,324
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 44.87
Granted (in dollars per share)	1.66
Canceled (in dollars per share)	50.59
Options Outstanding at the end of the period (in dollars per share)	44.65	$ 44.87
Options Vested and Expected to Vest at the end of the period (in dollars per share)	46.50
Options Exercisable at the end of the period (in dollars per share)	$ 118.98
Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at the end of the period	7 years 9 months 18 days	8 years
Options Vested and Expected to Vest at the end of the period	7 years 9 months 18 days
Options Exercisable at the end of the period	5 years 7 months 6 days

Stock-Based Compensation - Expenses (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Stock-based compensation expense
Weighted average grant-date fair value (in dollars per share)	$ 1.23
Stock-based compensation expense	$ 687	$ 1,693
Research and development
Stock-based compensation expense
Stock-based compensation expense	310	756
General and administrative
Stock-based compensation expense
Stock-based compensation expense	$ 377	$ 937

Stock-Based Compensation - Valuation (Details)	3 Months Ended
Stock-Based Compensation - Valuation (Details)	Mar. 31, 2020	Mar. 31, 2019
Black-Scholes option with following assumptions:
Expected stock price volatility (as a percent)	91.00%	91.00%
Expected option term	6 years	6 years
Risk-free interest rate (as a percent)	0.60%	2.50%
Expected dividend yield (as a percent)	0.00%	0.00%

Accumulated Other Comprehensive Income (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Accumulated Other Comprehensive Income
Period Start Balance	$ 94,026
Period End Balance	83,703
Amounts reclassified from AOCI	0
Unrealized Gain/(Loss) on Marketable Securities
Accumulated Other Comprehensive Income
Period Start Balance	23
Other comprehensive gain	(22)
Period End Balance	1
Foreign Currency Items
Accumulated Other Comprehensive Income
Period Start Balance	2,596
Period End Balance	2,596
Accumulated Other Comprehensive Income.
Accumulated Other Comprehensive Income
Period Start Balance	2,619
Other comprehensive gain	(22)
Period End Balance	$ 2,597

Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
Revenue (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Revenue
Accumulated Deficit	$ (1,025,941)		$ (1,013,316)
Accounts receivable	1,108		1,015
Contract liability	199		$ 254
Revenue, contract liabilities	100
Revenues	2,728	$ 1,425
Product Development and Licensing Agreements
Revenue
Revenues	2,286	129
Contracts and Grants
Revenue
Revenues	442	1,296
Rockefeller \| Product Development and Licensing Agreements
Revenue
Revenue, contract liabilities	1,800
Rockefeller University and Duke University \| Contracts and Grants
Revenue
Revenues	$ 400	$ 1,200

Income Taxes - Summary of Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Gross Deferred Tax Liabilities
Net Deferred Tax Liability	$ 3,007	$ 3,007

Net Loss Per Share (Details) - shares	3 Months Ended
Net Loss Per Share (Details) - shares	Mar. 31, 2020	Mar. 31, 2019
Anti-dilutive securities
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	1,659,251	839,656
Stock options
Anti-dilutive securities
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	1,658,141	836,104
Restricted Stock
Anti-dilutive securities
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	1,110	3,552

Kolltan Acquisition (Details) - USD ($) $ in Millions	Nov. 29, 2016	Mar. 31, 2020
Kolltan Acquisition
Shares issued as part of consideration (in shares)	1,217,200
Potential milestone payments	$ 172.5	$ 127.5