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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2020	Jul. 31, 2020
Document and Entity Information
Document Type	10-Q
Document Period End Date	Jun. 30, 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		39,126,448
Entity Central Index Key	0000744218
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current Assets:
Cash and Cash Equivalents	$ 68,027	$ 11,232
Marketable Securities	138,888	53,151
Accounts and Other Receivables	329	1,015
Prepaid and Other Current Assets	1,748	1,300
Total Current Assets	208,992	66,698
Property and Equipment, Net	4,044	4,031
Operating Lease Right-of-Use Assets, Net	3,134	3,473
Intangible Assets, Net	45,190	48,690
Other Assets	41	41
Total Assets	261,401	122,933
Current Liabilities:
Accounts Payable	950	1,174
Accrued Expenses	6,467	6,499
Current Portion of Operating Lease Liabilities	1,320	1,944
Current Portion of Other Long-Term Liabilities	2,104	2,026
Total Current Liabilities	10,841	11,643
Long-Term Portion of Operating Lease Liabilities	1,720	1,713
Other Long-Term Liabilities	10,396	15,551
Total Liabilities	22,957	28,907
Commitments and Contingent Liabilities
Stockholders' Equity:
Convertible Preferred Stock, $.01 Par Value; 3,000,000 Shares Authorized; No Shares Issued and Outstanding at June 30, 2020 and December 31, 2019
Common Stock, $.001 Par Value; 297,000,000 Shares Authorized; 39,093,868 and 16,972,077 Shares Issued and Outstanding at June 30, 2020 and December 31, 2019, Respectively	39	17
Additional Paid-In Capital	1,272,783	1,104,706
Accumulated Other Comprehensive Income	2,594	2,619
Accumulated Deficit	(1,036,972)	(1,013,316)
Total Stockholders' Equity	238,444	94,026
Total Liabilities and Stockholders' Equity	$ 261,401	$ 122,933

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
CONDENSED 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	39,093,868	16,972,077
Common Stock, Shares Outstanding	39,093,868	16,972,077

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
REVENUES:
Total Revenues	$ 236	$ 715	$ 2,965	$ 2,140
OPERATING EXPENSES:
Research and Development	9,705	10,081	21,400	21,232
General and Administrative	3,528	3,908	7,194	8,804
Intangible Asset Impairment	3,500		3,500
Other Asset Impairment				1,800
(Gain) Loss on Fair Value Remeasurement of Contingent Consideration	(5,132)	(1,017)	(4,898)	502
Total Operating Expenses	11,601	12,972	27,196	32,338
Operating Loss	(11,365)	(12,257)	(24,231)	(30,198)
Investment and Other Income, Net	106	478	347	1,180
Net Loss Before Income Tax Benefit	(11,259)	(11,779)	(23,884)	(29,018)
Income Tax Benefit	228		228
Net Loss	$ (11,031)	$ (11,779)	$ (23,656)	$ (29,018)
Basic and Diluted Net Loss Per Common Share	$ (0.50)	$ (0.84)	$ (1.20)	$ (2.21)
Shares Used in Calculating Basic and Diluted Net Loss Per Share	22,082	13,952	19,744	13,129
COMPREHENSIVE LOSS:
Net Loss	$ (11,031)	$ (11,779)	$ (23,656)	$ (29,018)
Other Comprehensive Income (Loss):
Unrealized (Loss) Gain on Marketable Securities	(3)	36	(25)	55
Comprehensive Loss	(11,034)	(11,743)	(23,681)	(28,963)
Product Development and Licensing Agreements
REVENUES:
Total Revenues		195	2,285	325
Contracts and Grants
REVENUES:
Total Revenues	$ 236	$ 520	$ 680	$ 1,815

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOW - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash Flows From Operating Activities:
Net Loss	$ (23,656)	$ (29,018)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	2,313	2,505
Amortization and Premium of Marketable Securities, Net	(335)	(652)
(Gain) Loss on Sale or Disposal of Assets	(20)	7
Intangible Asset Impairment	3,500
Other Asset Impairment		1,800
(Gain) Loss on Fair Value Remeasurement of Contingent Consideration	(4,898)	502
Non-Cash Income Tax Benefit	(228)
Stock-Based Compensation Expense	1,408	3,157
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	686	1,992
Prepaid and Other Current Assets	(436)	(137)
Accounts Payable and Accrued Expenses	(254)	(1,598)
Other Liabilities	(1,412)	(2,833)
Net Cash Used in Operating Activities	(23,332)	(24,275)
Cash Flows From Investing Activities:
Sales and Maturities of Marketable Securities	47,000	67,386
Purchases of Marketable Securities	(132,439)	(58,565)
Acquisition of Property and Equipment	(1,145)	(484)
Proceeds from Sale or Disposal of Assets	20
Net Cash (Used in) Provided by Investing Activities	(86,564)	8,337
Cash Flows From Financing Activities:
Net Proceeds from Stock Issuances	166,667	11,363
Proceeds from Issuance of Stock from Employee Benefit Plans	24	9
Issuance of Term Loan	2,962
Payment of Term Loan	(2,962)
Net Cash Provided by Financing Activities	166,691	11,372
Net Increase (Decrease) in Cash and Cash Equivalents	56,795	(4,566)
Cash and Cash Equivalents at Beginning of Period	11,232	24,310
Cash and Cash Equivalents at End of Period	68,027	19,744
Non-cash Investing Activities
Accrued construction in progress	$ 22	$ 55

Basis of Presentation	6 Months Ended
Basis of Presentation	Jun. 30, 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. At June 30, 2020, the Company had cash, cash equivalents and marketable securities of $206.9 million. The Company has had recurring losses and incurred a loss of $23.7 million for the six months ended June 30, 2020. Net cash used in operations for the six months ended June 30, 2020 was $23.3 million. The Company believes that the cash, cash equivalents and marketable securities at August 6, 2020 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 may take further steps to raise additional capital to meet its long-term 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. 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 hundreds of 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. In an effort to halt the outbreak of COVID-19, various states, including New Jersey, Massachusetts and Connecticut, where the Company has office, research and manufacturing facilities, 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 with a carrying value of $45.2 million at June 30, 2020.

Significant Accounting Policies	6 Months Ended
Significant Accounting Policies	Jun. 30, 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 and six months ended June 30, 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 six 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

6 Months Ended

Jun. 30, 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
	June 30, 2020		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	54,597		—	$	54,597		—
Marketable securities		138,888		—		138,888		—
	$	193,485		—	$	193,485		—
Liabilities:
Kolltan acquisition contingent consideration	$	7,587		—		—	$	7,587
	$	7,587		—		—	$	7,587


	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 six months ended June 30, 2020 (in thousands):


	Other Liabilities:
	Contingent
	Consideration
Balance at December 31, 2019	$	12,485
Fair value adjustments included in operating expenses		(4,898)
Balance at June 30, 2020	$	7,587

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 June 30, 2020, the weighted average discount rate used in calculating the fair value of contingent consideration was 11.6% (with a range of 11.5% to 12.2%) and the weighted average amount of time until the conditions of the milestone payments are met was 3 years.

During the three and six months ended June 30, 2020, the Company recorded a $5.1 million and $4.9 million gain on fair value remeasurement of contingent consideration, respectively, primarily due to updated assumptions for CDX-3379 related milestones due to the discontinuation of the CDX-3379 program and the passage of time. During the three and six months ended June 30, 2019, the Company recorded a $1.0 million gain and $0.5 million loss on fair value remeasurement of contingent consideration, respectively, 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 six months ended June 30, 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

6 Months Ended

Jun. 30, 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)
June 30, 2020
U.S. government and municipal obligations (maturing in one year or less)	$	79,937	$	—	$	—	$	79,937
Corporate debt securities (maturing in one year or less)		58,954		10		(13)		58,951
Total Marketable Securities	$	138,891	$	10	$	(13)	$	138,888

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 June 30, 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 June 30, 2020 and December 31, 2019.

Intangible Assets	6 Months Ended
Intangible Assets	Jun. 30, 2020
Intangible Assets
Intangible Assets	(5) Intangible Assets At June 30, 2020 and December 31, 2019, the Company recorded indefinite-lived intangible assets of $45.2 million and $48.7 million, respectively. 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.The Company evaluated the CDX-3379 IPR&D asset for potential impairment as a result of the discontinuation of the CDX-3379 program. The Company concluded that the CDX-3379 IPR&D asset was fully impaired, and a non-cash impairment charge of $3.5 million was recorded for the three months ended June 30, 2020. CDX-0159 is in Phase 1 development and the TAM program is in preclinical development. As of June 30, 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	6 Months Ended
Other Assets	Jun. 30, 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. The Company assesses the private company's financial condition on a quarterly basis. There was no change in the value of the investment during the six months ended June 30, 2020.

Other Long-Term Liabilities

6 Months Ended

Jun. 30, 2020

Other Long-Term Liabilities

Other Long-Term Liabilities

(7) Other Long-Term Liabilities

Other long-term liabilities include the following:


	June 30, 2020		December 31, 2019
	(In thousands)
Net Deferred Tax Liabilities Related to IPR&D (Note 12)	$	2,779	$	3,007
Deferred Income From Sale of Tax Benefits		1,831		1,831
Contingent Milestones (Note 3)		7,587		12,485
Deferred Revenue (Note 11)		303		254
Total		12,500		17,577
Less Current Portion		(2,104)		(2,026)
Long-Term Portion	$	10,396	$	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 in other income related to the sale of these tax benefits during the three and six months ended June 30, 2020 and $0.0 million and $0.2 million during the three and six months ended June 30, 2019, respectively.

Stockholders' Equity

6 Months Ended

Jun. 30, 2020

Stockholders' Equity

Stockholders' Equity

(8) Stockholders’ Equity

In May 2016, the Company entered into a controlled equity offering sales 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. During the six months ended June 30, 2020, the Company issued 6.7 million shares of common stock pursuant to the Cantor Agreement resulting in net proceeds of $25.3 million after deducting commission and offering expenses. At June 30, 2020, the Company had $18.3 million remaining in aggregate gross offering price available under a prospectus supplement filed pursuant to the agreement.

During the three months ended June 30, 2020, the Company issued 15,384,614 shares of its common stock in an underwritten public offering resulting in net proceeds to the Company of $141.4 million, after deducting underwriting fees and offering expenses.

The changes in Stockholders’ Equity during the three and six months ended June 30, 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
Shares Issued in Connection with Cantor Agreement	5,978,452		6		23,686		—		—		23,692
Shares Issued in Underwritten Offering	15,384,614		15		141,346		—		—		141,361
Share-Based Compensation	—		—		722		—		—		722
Unrealized Loss on Marketable Securities	—		—		—		(3)		—		(3)
Net Loss	—		—		—		—		(11,031)		(11,031)
Consolidated Balance at June 30, 2020	39,093,868	$	39	$	1,272,783	$	2,594	$	(1,036,972)	$	238,444

						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 Gain 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
Shares Cancelled under Stock Option and Employee Stock Purchase Plans	(222)		—		—		—		—		—
Shares Issued in Connection with Cantor Agreement	1,972,428		2		7,210		—		—		7,212
Share-Based Compensation	—		—		1,464		—		—		1,464
Unrealized Gain on Marketable Securities	—		—		—		36		—		36
Net Loss	—		—		—		—		(11,779)		(11,779)
Consolidated Balance at June 30, 2019	14,816,917	$	15	$	1,098,429	$	2,638	$	(991,456)	$	109,626

Stock-Based Compensation

6 Months Ended

Jun. 30, 2020

Stock-Based Compensation

Stock-Based Compensation

(9) Stock-Based Compensation

A summary of stock option activity for the six months ended June 30, 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	1,439,175	$	10.36
Exercised	—		—
Canceled	(53,090)	$	46.03
Options Outstanding at June 30, 2020	3,085,287	$	28.76	8.69
Options Vested and Expected to Vest at June 30, 2020	2,875,684	$	30.23	8.62
Options Exercisable at June 30, 2020	821,537	$	84.93	6.39
Shares Available for Grant Under the 2008 Plan	938,178

The weighted average grant-date fair value of stock options granted during the three and six month period ended June 30, 2020 was $7.96 and $7.95, respectively. Stock-based compensation expense for the three and six months ended June 30, 2020 and 2019 was recorded as follows:


	Three months ended June 30,				Six months ended June 30,
	2020		2019		2020		2019
	(In thousands)				(In thousands)
Research and development	$	342	$	654	$	652	$	1,410
General and administrative		380		810		756		1,747
Total stock-based compensation expense	$	722	$	1,464	$	1,408	$	3,157

The fair values of employee and director stock options granted during the three and six months ended June 30, 2020 and 2019 were valued using the Black-Scholes option pricing model with the following assumptions:


	Three months ended June 30,				Six months ended June 30,
	2020		2019		2020		2019
Expected stock price volatility	97	%	91	%	91 - 97	%	91	%
Expected option term	6.0	Years	6.0	Years	6.0	Years	6.0	Years
Risk-free interest rate	0.5	%	1.9 - 2.4	%	0.5 - 0.6	%	1.9 - 2.5	%
Expected dividend yield	None		None		None		None

Accumulated Other Comprehensive Income

6 Months Ended

Jun. 30, 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 six months ended June 30, 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		(25)		—		(25)
Balance at June 30, 2020	$	(2)	$	2,596	$	2,594

No amounts were reclassified out of accumulated other comprehensive income during the six months ended June 30, 2020.

Revenue	6 Months Ended
Revenue	Jun. 30, 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 first quarter of 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 or at a negotiated fixed-price. The Company recognized $0.2 million and $0.5 million in revenue under these agreements during the three and six months ended June 30, 2020, respectively, and $0.4 million and $1.5 million during the three and six months ended June 30, 2019, respectively. Contract Assets and Liabilities At December 31, 2019 and June 30, 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 June 30, 2020, the Company had $0.3 million in contract liabilities recorded. Revenue recognized from contract liabilities as of December 31, 2019 during the three and six months ended June 30, 2020 was $0.0 million and $0.1 million, respectively.

Income Taxes	6 Months Ended
Income Taxes	Jun. 30, 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 June 30, 2020 and December 31, 2019. The net deferred tax liability of $2.8 million and $3.0 million at June 30, 2020 and December 31, 2019,respectively, relates to the temporary differences associated with the IPR&D intangible assets acquired in previous business combinations and is not deductible for tax purposes. During the quarter ended June 30, 2020, a $0.2 million non-cash income tax benefit was recorded related to the impairment of the CDX-3379 IPR&D asset. 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

6 Months Ended

Jun. 30, 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:


	Six Months Ended June 30,
	2020	2019
Stock Options	3,085,287	1,690,074
Restricted Stock	—	1,110
	3,085,287	1,691,184

Kolltan Acquisition	6 Months Ended
Kolltan Acquisition	Jun. 30, 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 June 30, 2020, the Company believes that the adjusted amount we may be required to pay for future consideration is up to $107.5 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 continuting to discuss 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)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 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)

6 Months Ended

Jun. 30, 2020

Fair Value Measurements

Schedule of financial assets and liabilities subject to fair value measurements


	As of
	June 30, 2020		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds and cash equivalents	$	54,597		—	$	54,597		—
Marketable securities		138,888		—		138,888		—
	$	193,485		—	$	193,485		—
Liabilities:
Kolltan acquisition contingent consideration	$	7,587		—		—	$	7,587
	$	7,587		—		—	$	7,587


	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

The following table reflects the activity for the Company’s contingent consideration liabilities measured at fair value using Level 3 inputs for the six months ended June 30, 2020 (in thousands):


	Other Liabilities:
	Contingent
	Consideration
Balance at December 31, 2019	$	12,485
Fair value adjustments included in operating expenses		(4,898)
Balance at June 30, 2020	$	7,587

Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2020

Marketable Securities

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


	Gross Unrealized
	Amortized						Fair
	Cost		Gains		Losses		Value
	(In thousands)
June 30, 2020
U.S. government and municipal obligations (maturing in one year or less)	$	79,937	$	—	$	—	$	79,937
Corporate debt securities (maturing in one year or less)		58,954		10		(13)		58,951
Total Marketable Securities	$	138,891	$	10	$	(13)	$	138,888

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)

6 Months Ended

Jun. 30, 2020

Other Long-Term Liabilities

Schedule of other long-term liabilities


	June 30, 2020		December 31, 2019
	(In thousands)
Net Deferred Tax Liabilities Related to IPR&D (Note 12)	$	2,779	$	3,007
Deferred Income From Sale of Tax Benefits		1,831		1,831
Contingent Milestones (Note 3)		7,587		12,485
Deferred Revenue (Note 11)		303		254
Total		12,500		17,577
Less Current Portion		(2,104)		(2,026)
Long-Term Portion	$	10,396	$	15,551

Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 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
Shares Issued in Connection with Cantor Agreement	5,978,452		6		23,686		—		—		23,692
Shares Issued in Underwritten Offering	15,384,614		15		141,346		—		—		141,361
Share-Based Compensation	—		—		722		—		—		722
Unrealized Loss on Marketable Securities	—		—		—		(3)		—		(3)
Net Loss	—		—		—		—		(11,031)		(11,031)
Consolidated Balance at June 30, 2020	39,093,868	$	39	$	1,272,783	$	2,594	$	(1,036,972)	$	238,444

						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 Gain 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
Shares Cancelled under Stock Option and Employee Stock Purchase Plans	(222)		—		—		—		—		—
Shares Issued in Connection with Cantor Agreement	1,972,428		2		7,210		—		—		7,212
Share-Based Compensation	—		—		1,464		—		—		1,464
Unrealized Gain on Marketable Securities	—		—		—		36		—		36
Net Loss	—		—		—		—		(11,779)		(11,779)
Consolidated Balance at June 30, 2019	14,816,917	$	15	$	1,098,429	$	2,638	$	(991,456)	$	109,626

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 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	1,439,175	$	10.36
Exercised	—		—
Canceled	(53,090)	$	46.03
Options Outstanding at June 30, 2020	3,085,287	$	28.76	8.69
Options Vested and Expected to Vest at June 30, 2020	2,875,684	$	30.23	8.62
Options Exercisable at June 30, 2020	821,537	$	84.93	6.39
Shares Available for Grant Under the 2008 Plan	938,178

Schedule of stock-based compensation expense


	Three months ended June 30,				Six months ended June 30,
	2020		2019		2020		2019
	(In thousands)				(In thousands)
Research and development	$	342	$	654	$	652	$	1,410
General and administrative		380		810		756		1,747
Total stock-based compensation expense	$	722	$	1,464	$	1,408	$	3,157

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


	Three months ended June 30,				Six months ended June 30,
	2020		2019		2020		2019
Expected stock price volatility	97	%	91	%	91 - 97	%	91	%
Expected option term	6.0	Years	6.0	Years	6.0	Years	6.0	Years
Risk-free interest rate	0.5	%	1.9 - 2.4	%	0.5 - 0.6	%	1.9 - 2.5	%
Expected dividend yield	None		None		None		None

Accumulated Other Comprehensive Income (Tables)

6 Months Ended

Jun. 30, 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		(25)		—		(25)
Balance at June 30, 2020	$	(2)	$	2,596	$	2,594

Net Loss Per Share (Tables)

6 Months Ended

Jun. 30, 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


	Six Months Ended June 30,
	2020	2019
Stock Options	3,085,287	1,690,074
Restricted Stock	—	1,110
	3,085,287	1,691,184

Basis of Presentation (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
Basis of Presentation (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 206,900				$ 206,900
Net Loss	(11,031)	$ (12,625)	$ (11,779)	$ (17,239)	(23,656)	$ (29,018)
Net cash used in operations					23,332	$ 24,275
Indefinite-lived intangible assets	$ 45,200				$ 45,200		$ 48,700

Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Liabilities:
Kolltan acquisition contingent consideration	$ 7,587	$ 12,485
Fair value \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	7,587	12,485
Fair Value Measurements. \| Level 2
Assets:
Money market funds and cash equivalents	54,597	4,024
Marketable securities	138,888	53,151
Total financial assets at fair value	193,485	57,175
Fair Value Measurements. \| Level 3
Liabilities:
Kolltan acquisition contingent consideration	7,587	12,485
Total financial liabilities at fair value	7,587	12,485
Fair Value Measurements. \| Fair value
Assets:
Money market funds and cash equivalents	54,597	4,024
Marketable securities	138,888	53,151
Total financial assets at fair value	193,485	57,175
Liabilities:
Kolltan acquisition contingent consideration	7,587	12,485
Total financial liabilities at fair value	$ 7,587	$ 12,485

Fair Value Measurements - Contingent Consideration Liabilities (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)
Contingent consideration liabilities measured at fair value
Balance at beginning of period	$ 12,485
Balance at end of period	7,587
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	(4,898)
Balance at end of period	$ 7,587

Fair Value Measurements - Additional information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) Y	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) Y	Jun. 30, 2019 USD ($)
Fair value measurements
(Gain) Loss on Fair Value Remeasurement of Contingent Consideration	$ (5,132)	$ (1,017)	$ (4,898)	$ 502
Discount rate \| Weighted average
Fair value measurements
Measurement input	11.6		11.6
Discount rate \| Minimum
Fair value measurements
Measurement input	11.5		11.5
Discount rate \| Maximum
Fair value measurements
Measurement input	12.2		12.2
Time until the conditions of the milestone payments are met
Fair value measurements
Measurement input \| Y	3		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	Jun. 30, 2020	Dec. 31, 2019
Amortized Cost
Amortized Cost	$ 138,891	$ 53,128
Gross Unrealized Gains
Gross Unrealized Gains	10	26
Gross Unrealized Losses
Gross Unrealized Losses	(13)	(3)
Fair Value
Fair Value	138,888	53,151
U.S. government and municipal obligations
Amortized Cost
Maturing in one year or less	79,937	18,509
Gross Unrealized Gains
Maturing in one year or less		13
Fair Value
Maturing in one year or less	79,937	18,522
Corporate debt securities
Amortized Cost
Maturing in one year or less	58,954	34,619
Gross Unrealized Gains
Maturing in one year or less	10	13
Gross Unrealized Losses
Maturing in one year or less	(13)	(3)
Fair Value
Maturing in one year or less	$ 58,951	$ 34,629

Marketable Securities - Additional Information (Details) - USD ($) $ in Thousands	Jun. 30, 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 Thousands	3 Months Ended	6 Months Ended
Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Intangible Assets
Indefinite-lived intangible assets	$ 45,200	$ 45,200	$ 48,700
Non-cash impairment charge, indefinite-lived	$ 3,500	$ 3,500

Other Assets (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
Other Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jun. 30, 2020	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
Change in the value of investments		$ 0.0

Other Long-Term Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Other Long-Term Liabilities
Net Deferred Tax Liabilities Related to IPR&D (Note 12)	$ 2,779	$ 3,007
Deferred Income From Sale of Tax Benefits	1,831	1,831
Contingent Milestones (Note 3)	7,587	12,485
Deferred Revenue (Note 11)	303	254
Total	12,500	17,577
Less Current Portion	(2,104)	(2,026)
Long-Term Portion	$ 10,396	$ 15,551

Other Long-Term Liabilities- New Jersey tax benefits (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Nov. 30, 2015	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investment and other income		$ 106	$ 478	$ 347	$ 1,180
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	$ 0	$ 0	$ 200

Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
Stockholders' Equity (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Common Stock
Period Start Balance	$ 83,703	$ 94,026	$ 112,693	$ 124,060	$ 94,026	$ 124,060
Balance (in shares)		16,972,077			16,972,077
Shares Issued under Stock Option and Employee Stock Purchase Plans		$ 24		9
Shares Issued In Connection With Cantor Agreement	23,692	1,614	7,212	4,151
Shares Issued in Underwritten Offering	141,361
Share-Based Compensation	722	686	1,464	1,693
Unrealized (Loss) Gain on Marketable Securities	(3)	(22)	36	19	$ (25)	55
Net Loss	(11,031)	(12,625)	(11,779)	(17,239)	(23,656)	(29,018)
Period End Balance	$ 238,444	83,703	109,626	112,693	$ 238,444	109,626
Balance (in shares)	39,093,868				39,093,868
Net proceeds from sale of common stock					$ 166,667	11,363
Underwritten Public Offering
Common Stock
Common stock issued (in shares)	15,384,614
Net proceeds from sale of common stock	$ 141,400
Common Stock
Common Stock
Period Start Balance	$ 18	$ 17	$ 13	$ 12	$ 17	$ 12
Balance (in shares)	17,730,802	16,972,077	12,844,711	11,957,635	16,972,077	11,957,635
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)		12,573		3,507
Shares Cancelled under Stock Option and employee Stock Purchase Plans			(222)
Shares Issued In Connection With Cantor Agreement	$ 6	$ 1	$ 2	$ 1
Shares Issued in Connection with Cantor Agreement (in shares)	5,978,452	746,152	1,972,428	883,569	6,700,000
Shares Issued in Underwritten Offering	$ 15
Shares Issued in Underwritten Offering (in shares)	15,384,614
Period End Balance	$ 39	$ 18	$ 15	$ 13	$ 39	$ 15
Balance (in shares)	39,093,868	17,730,802	14,816,917	12,844,711	39,093,868	14,816,917
Net proceeds from sale of common stock					$ 25,300
Aggregate gross offering price available	$ 18,300				18,300
Additional Paid-In Capital
Common Stock
Period Start Balance	1,107,029	$ 1,104,706	$ 1,089,755	$ 1,083,903	1,104,706	$ 1,083,903
Shares Issued under Stock Option and Employee Stock Purchase Plans		24		9
Shares Issued In Connection With Cantor Agreement	23,686	1,613	7,210	4,150
Shares Issued in Underwritten Offering	141,346
Share-Based Compensation	722	686	1,464	1,693
Period End Balance	1,272,783	1,107,029	1,098,429	1,089,755	1,272,783	1,098,429
Accumulated Other Comprehensive Income.
Common Stock
Period Start Balance	2,597	2,619	2,602	2,583	2,619	2,583
Unrealized (Loss) Gain on Marketable Securities	(3)	(22)	36	19
Period End Balance	2,594	2,597	2,638	2,602	2,594	2,638
Accumulated Deficit
Common Stock
Period Start Balance	(1,025,941)	(1,013,316)	(979,677)	(962,438)	(1,013,316)	(962,438)
Net Loss	(11,031)	(12,625)	(11,779)	(17,239)
Period End Balance	$ (1,036,972)	$ (1,025,941)	$ (991,456)	$ (979,677)	$ (1,036,972)	$ (991,456)

Stock-Based Compensation - Stock Option Activity (Details) - Stock options - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Shares
Options Outstanding at beginning of the period (in shares)	1,699,202
Granted (in shares)	1,439,175
Canceled (in shares)	(53,090)
Options Outstanding at the end of the period (in shares)	3,085,287	1,699,202
Options Vested and Expected to Vest at the end of the period (in shares)	2,875,684
Options Exercisable at the end of the period (in shares)	821,537
Shares Available for Grant Under the 2008 Plan	938,178
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 44.87
Granted (in dollars per share)	10.36
Canceled (in dollars per share)	46.03
Options Outstanding at the end of the period (in dollars per share)	28.76	$ 44.87
Options Vested and Expected to Vest at the end of the period (in dollars per share)	30.23
Options Exercisable at the end of the period (in dollars per share)	$ 84.93
Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at the end of the period	8 years 8 months 9 days	8 years
Options Vested and Expected to Vest at the end of the period	8 years 7 months 13 days
Options Exercisable at the end of the period	6 years 4 months 21 days

Stock-Based Compensation - Expenses (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock-based compensation expense
Weighted average grant-date fair value (in dollars per share)	$ 7.96		$ 7.95
Stock-based compensation expense	$ 722	$ 1,464	$ 1,408	$ 3,157
Research and development
Stock-based compensation expense
Stock-based compensation expense	342	654	652	1,410
General and administrative
Stock-based compensation expense
Stock-based compensation expense	$ 380	$ 810	$ 756	$ 1,747

Stock-Based Compensation - Valuation (Details)	3 Months Ended		6 Months Ended
Stock-Based Compensation - Valuation (Details)	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Black-Scholes option with following assumptions:
Expected stock price volatility (as a percent)	97.00%	91.00%		91.00%
Expected stock price volatility, minimum (as a percent)			91.00%
Expected stock price volatility, maximum (as a percent)			97.00%
Expected option term	6 years	6 years	6 years	6 years
Risk-free interest rate (as a percent)	0.50%
Risk-free interest rate, minimum (as a percent)		1.90%	0.50%	1.90%
Risk-free interest rate, maximum (as a percent)		2.40%	0.60%	2.50%
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%	0.00%

Accumulated Other Comprehensive Income (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)
Accumulated Other Comprehensive Income
Period Start Balance	$ 94,026
Period End Balance	238,444
Amounts reclassified from AOCI	0
Unrealized Gain/(Loss) on Marketable Securities
Accumulated Other Comprehensive Income
Period Start Balance	23
Other comprehensive loss	(25)
Period End Balance	(2)
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 loss	(25)
Period End Balance	$ 2,594

Revenue (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
Revenue (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Revenue
Accumulated Deficit	$ (1,036,972)			$ (1,036,972)		$ (1,013,316)
Accounts receivable	329			329		1,015
Contract assets	0			0		0
Contract liability	303			303		$ 254
Revenue, contract liabilities	0			100
Revenues	236		$ 715	2,965	$ 2,140
Product Development and Licensing Agreements
Revenue
Revenues			195	2,285	325
Contracts and Grants
Revenue
Revenues	236		520	680	1,815
Rockefeller \| Product Development and Licensing Agreements
Revenue
Revenue, contract liabilities		$ 1,800
Rockefeller University and Duke University \| Contracts and Grants
Revenue
Revenues	$ 200		$ 400	$ 500	$ 1,500

Income Taxes - Summary of Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Gross Deferred Tax Liabilities
Net Deferred Tax Liability	$ 2,779	$ 2,779	$ 3,007
Principal components of the deferred tax assets and liabilities
Income Tax Benefit	$ (228)	$ (228)

Net Loss Per Share (Details) - shares	6 Months Ended
Net Loss Per Share (Details) - shares	Jun. 30, 2020	Jun. 30, 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	3,085,287	1,691,184
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	3,085,287	1,690,074
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

Kolltan Acquisition (Details) - USD ($) $ in Millions	Nov. 29, 2016	Jun. 30, 2020
Kolltan Acquisition
Shares issued as part of consideration (in shares)	1,217,200
Potential milestone payments	$ 172.5	$ 107.5