Celldex Therapeutics (CLDX) 10-K 7 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 28, 2019	Jun. 30, 2018
Document and Entity Information
Entity Registrant Name	Celldex Therapeutics, Inc.
Entity Central Index Key	744,218
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Public Float			$ 79
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		12,439,730
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and Cash Equivalents	$ 24,310	$ 40,288
Marketable Securities	69,712	99,139
Accounts and Other Receivables	3,162	1,880
Prepaid and Other Current Assets	1,895	3,449
Total Current Assets	99,079	144,756
Property and Equipment, Net	6,111	10,372
Intangible Assets, Net	48,690	67,591
Other Assets	1,929	1,929
Goodwill		90,976
Total Assets	155,809	315,624
Current Liabilities:
Accounts Payable	1,069	1,715
Accrued Expenses	7,007	19,455
Current Portion of Long-Term Liabilities	4,526	6,566
Total Current Liabilities	12,602	27,736
Other Long-Term Liabilities	19,147	51,519
Total Liabilities	31,749	79,255
Commitments and Contingent Liabilities (Notes 13 and 15)
Stockholders' Equity:
Convertible Preferred Stock, $.01 Par Value; 3,000,000 Shares Authorized; No Shares Issued and Outstanding at September 30, 2018 and December 31, 2017
Common Stock, $.001 Par Value; 297,000,000 Shares Authorized; 11,957,635 and 9,234,693 Shares Issued and Outstanding at December 31, 2018 and 2017, Respectively	12	9
Additional Paid-In Capital	1,083,903	1,046,313
Accumulated Other Comprehensive Income	2,583	2,564
Accumulated Deficit	(962,438)	(812,517)
Total Stockholders' Equity	124,060	236,369
Total Liabilities and Stockholders' Equity	$ 155,809	$ 315,624

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
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	11,957,635	9,234,693
Common Stock, Shares Outstanding	11,957,635	9,234,693

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
REVENUES:
Total Revenues	$ 9,538	$ 12,743	$ 6,786
OPERATING EXPENSES:
Research and Development	66,449	96,171	102,726
General and Administrative	19,269	25,003	35,979
Goodwill Impairment	90,976
Intangible Asset Impairment	18,677	13,000
Gain on Fair Value Remeasurement of Contingent Consideration	(29,621)	(800)
Amortization of Acquired Intangible Assets	224	896	997
Total Operating Expenses	165,974	134,270	139,702
Operating Loss	(156,436)	(121,527)	(132,916)
Investment and Other Income, Net	4,487	4,214	4,386
Net Loss Before Income Tax Benefit	(151,949)	(117,313)	(128,530)
Income Tax Benefit	765	24,282
Net Loss	$ (151,184)	$ (93,031)	$ (128,530)
Basic and Diluted Net Loss Per Common Share (in dollars per share)	$ (14.48)	$ (10.86)	$ (18.99)
Shares Used in Calculating Basic and Diluted Net Loss Per Share (in shares)	10,442	8,570	6,769
COMPREHENSIVE LOSS:
Net Loss	$ (151,184)	$ (93,031)	$ (128,530)
Other Comprehensive Income (Loss):
Unrealized Gain (Loss) on Marketable Securities	19	23	234
Comprehensive Loss	(151,165)	(93,008)	(128,296)
Product Development and Licensing Agreements
REVENUES:
Total Revenues	3,341	3,153	2,174
Contracts and Grants
REVENUES:
Total Revenues	$ 6,197	$ 9,590	$ 4,612

STATEMENTS OF STOCKHOLDERS' EQU

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated DeficitASC 606	Accumulated Deficit	ASC 606	Total
Period Start Balance at Dec. 31, 2015	$ 7	$ 878,747	$ 2,307		$ (590,956)		$ 290,105
Balance (in shares) at Dec. 31, 2015	6,579,040
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans		535					535
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	10,543
Shares Issued in Connection with Cantor Agreement		13,946					13,946
Shares Issued in Connection with Cantor Agreement (in shares)	220,253
Shares Issued in Connection with the Kolltan Acquisition	$ 1	73,396					73,397
Shares Issued in Connection with the Kolltan Acquisition (in shares)	1,217,200
Shares Issued in Connection with Kolltan Severance		427					427
Shares Issued in Connection with Kolltan Severance (in shares)	7,407
Share-Based Compensation		15,317					15,317
Unrealized Gains on Marketable Securities			234				234
Net Loss					(128,530)		(128,530)
Period End Balance at Dec. 31, 2016	$ 8	982,368	2,541		(719,486)		265,431
Balance (in shares) at Dec. 31, 2016	8,034,443
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans		265					265
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	11,581
Shares Issued in Connection with Cantor Agreement	$ 1	51,024					51,025
Shares Issued in Connection with Cantor Agreement (in shares)	1,181,524
Shares Issued in Connection with Kolltan Severance		344					344
Shares Issued in Connection with Kolltan Severance (in shares)	7,145
Share-Based Compensation		12,312					12,312
Unrealized Gains on Marketable Securities			23				23
Net Loss					(93,031)		(93,031)
Period End Balance at Dec. 31, 2017	$ 9	1,046,313	2,564		(812,517)		$ 236,369
Balance (in shares) at Dec. 31, 2017	9,234,693						9,234,693
Increase (Decrease) in Stockholders' Equity
Shares Issued under Stock Option and Employee Stock Purchase Plans		419					$ 419
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	16,047
Shares Issued in Connection with Cantor Agreement	$ 3	29,019					29,022
Shares Issued in Connection with Cantor Agreement (in shares)	2,702,660
Shares Issued in Connection with Kolltan Severance		71					71
Shares Issued in Connection with Kolltan Severance (in shares)	4,235
Share-Based Compensation		8,081					8,081
Unrealized Gains on Marketable Securities			19				19
Adoption of ASC 606				$ 1,263		$ 1,263
Net Loss					(151,184)		(151,184)
Period End Balance at Dec. 31, 2018	$ 12	$ 1,083,903	$ 2,583		$ (962,438)		$ 124,060
Balance (in shares) at Dec. 31, 2018	11,957,635						11,957,635

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows From Operating Activities:
Net Loss	$ (151,184)	$ (93,031)	$ (128,530)
Adjustments to Reconcile Net Loss to Net Cash Used in Operating Activities:
Depreciation and Amortization	3,577	4,414	3,095
Amortization of Intangible Assets	224	896	997
Amortization and Premium of Marketable Securities, Net	(1,048)	(290)	926
Loss on Sale or Disposal of Assets	1,220	55	81
Goodwill Impairment	90,976
Intangible Asset Impairment	18,677	13,000
Gain on Fair Value Remeasurement of Contingent Consideration	(29,621)	(800)
Non-Cash Income Tax Benefit	(765)	(24,282)
Stock-Based Compensation Expense	8,081	12,312	15,317
Non-Cash Expense			1,638
Changes in Operating Assets and Liabilities:
Accounts and Other Receivables	(777)	(96)	(814)
Prepaid and Other Current Assets	1,783	793	1,320
Other Assets		205	(89)
Accounts Payable and Accrued Expenses	(13,110)	(8,744)	(4,970)
Other Liabilities	(3,268)	(4,363)	(2,007)
Net Cash Used in Operating Activities	(75,235)	(99,931)	(113,036)
Cash Flows From Investing Activities:
Sales and Maturities of Marketable Securities	201,469	219,236	242,792
Purchases of Marketable Securities	(171,182)	(170,980)	(173,925)
Investment in Other			(1,801)
Cash Acquired in Kolltan Acquisition, Net			4,592
Acquisition of Property and Equipment	(813)	(1,788)	(2,751)
Proceeds from Sale or Disposal of Assets	342
Net Cash Provided by Investing Activities	29,816	46,468	68,907
Cash Flows From Financing Activities:
Net Proceeds from Stock Issuances	29,022	51,025	13,946
Proceeds from Issuance of Stock from Employee Benefit Plans	419	265	536
Net Cash Provided by Financing Activities	29,441	51,290	14,482
Net Decrease in Cash and Cash Equivalents	(15,978)	(2,173)	(29,647)
Cash and Cash Equivalents at Beginning of Period	40,288	42,461	72,108
Cash and Cash Equivalents at End of Period	24,310	40,288	42,461
Non-cash Investing Activities
Accrued construction in progress	107	20	159
Non-cash Supplemental Disclosure
Shares issued to former Kolltan executive for settlement of severance	$ 71	$ 344	426
Shares issued in connection with Kolltan Acquisition			$ 73,397

Nature of Business and Overview

Nature of Business and Overview	12 Months Ended
	Dec. 31, 2018
Nature of Business and Overview
Nature of Business and Overview	(1) Nature of Business and Overview Celldex Therapeutics, Inc. (the “Company” or “Celldex”) is a biopharmaceutical company focused on the development and commercialization of several immunotherapy technologies and other cancer-targeting biologics. The Company currently has four drug candidates in clinical development, including CDX-1140, CDX-3379,varlilumab (also referred to as CDX-1127), and CDX-301. At December 31, 2018, the Company had cash, cash equivalents and marketable securities of $94.0 million. The Company has had recurring losses and incurred a loss of $151.2 million for the year ended December 31, 2018. Net cash used in operations for the year ended December 31, 2018 was $75.2 million. The Company believes that the cash, cash equivalents and marketable securities at March 7, 2019 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. The Board of Directors of the Company approved a one for fifteen reverse stock split of the Company’s outstanding common stock, which was effected on February 8, 2019. All share and per share amounts in the financial statements have been retroactively adjusted for all periods presented to give effect to the reverse stock split, including reclassifying an amount equal to the reduction in par value to additional paid-in capital. During the next twelve months and beyond, the Company will take further steps to raise additional capital to meet its liquidity needs. These capital raising activities may include, but may not be limited to, one or more of the following: the licensing of drug candidates with existing or new collaborative partners, possible business combinations, issuance of debt, or the issuance of common stock or other securities via private placements or public offerings. While the Company may seek capital through a number of means, there can be no assurance that additional financing will be available on acceptable terms, if at all, and the Company's negotiating position in capital-raising efforts may worsen as existing resources are used. There is also no assurance that the Company will be able to enter into further collaborative relationships. Additional equity financings may be dilutive to the Company's stockholders; debt financing, if available, may involve significant cash payment obligations and covenants that restrict the Company's ability to operate as a business; and licensing or strategic collaborations may result in royalties or other terms which reduce the Company's economic potential from products under development. The Company's ability to continue funding its planned operations into and beyond twelve months from the issuance date is also dependent on the timing and manner of payment of future contingent milestones from the Kolltan acquisition, in the event that the Company achieves the drug candidate milestones related to those payments. The Company, at its option, may decide to pay those milestone payments in cash, shares of its common stock or a combination thereof. If the Company is unable to raise the funds necessary to meet its liquidity needs, it may have to delay or discontinue the development of one or more programs, discontinue or delay ongoing or anticipated clinical trials, license out programs earlier than expected, raise funds at a significant discount or on other unfavorable terms, if at all, or sell all or a part of the Company.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	(2) Summary of Significant Accounting Policies Basis of Presentation The balance sheets and statements of operations and comprehensive loss, stockholders’ equity, and cash flows, are consolidated for the years ended December 31, 2018 and 2017. These consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company operates in one segment, which is the business of development, manufacturing and commercialization of novel therapeutics for human health care. Use of Estimates The preparation of the financial statements in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP) requires management to make estimates and use assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the dates of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with a maturity date of 90 days or less at the date of purchase to be cash equivalents. Cash equivalents consist principally of money market funds and debt securities. Marketable Securities The Company invests its excess cash balances in marketable securities, including municipal bond securities, U.S. government agency securities, and highly rated corporate bonds. The Company classifies all of its marketable securities as current assets on the balance sheets because they are available-for-sale and available to fund current operations. Marketable securities are stated at fair value with unrealized gains and losses included as a component of accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity, until such gains and losses are realized. If a decline in the fair value is considered other-than-temporary, based on available evidence, the unrealized loss is reclassified from accumulated other comprehensive income (loss) to the statements of operations. Realized gains and losses are determined on the specific identification method and are included in investment and other income, net. Concentration of Credit Risk and of Significant Customers and Suppliers Financial instruments that potentially subject the Company to concentrations of credit risk primarily consist of cash, cash equivalents, marketable securities and accounts receivable. The Company invests its cash, cash equivalents and marketable securities in debt instruments and interest-bearing accounts at major financial institutions in excess of insured limits. The Company mitigates credit risk by limiting the investment type and maturity to securities that preserve capital, maintain liquidity and have a high credit quality. The Company has not historically experienced credit losses from its accounts receivable and therefore has not established an allowance for doubtful accounts. Combined revenue from BMS, Rockefeller and International AIDS Vaccine Initiative represented 86% of total Company revenue for the year ended December 31, 2018 and 77% of total Company revenue for the year ended December 31, 2017. Combined revenue from Rockefeller and BMS represented 71% of total Company revenue for the year ended December 31, 2016. The Company relies on contract manufacturing organizations (CMO) to manufacture drug substance and drug product as well as for future commercial supplies. The Company also relies on CMOs for supply of raw materials as well as filling, packaging, storing and shipping our drug products. The Company relies on third‑party collaborators to develop companion diagnostic tests. Fair Value Measurements The Company has certain assets and liabilities that are measured at fair value in the financial statements. The Company seeks to maximize the use of observable inputs (market data obtained from sources independent from the Company) and to minimize the use of unobservable inputs (the Company’s assumptions about how market participants would price assets and liabilities) when measuring the fair value of its assets and liabilities. These assets and liabilities are classified into one of three levels of the following fair value hierarchy as defined by U.S. GAAP: Level 1: Observable inputs such as quoted prices in active markets for identical assets or liabilities. An active market for an asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2: Observable inputs other than Level 1 prices, such as quoted prices in active markets for similar assets or liabilities and quoted prices for identical assets or liabilities in markets that are not active. Level 3: Unobservable inputs based on the Company’s assessment of the assumptions that market participants would use in pricing the asset or liability. Property and Equipment Property and equipment is stated at cost and depreciated over the estimated useful lives of the related assets using the straight‑line method. Laboratory equipment and office furniture and equipment are depreciated over five years, and computer equipment is depreciated over three years. Manufacturing equipment is amortized over seven to ten years. Leasehold improvements are amortized over the shorter of the estimated useful life or the non‑cancelable term of the related lease, including any renewals that are reasonably assured of occurring. Property and equipment under construction is classified as construction in progress and is depreciated or amortized only after the asset is placed in service. Expenditures for maintenance and repairs are charged to expense whereas the costs of significant improvements which extend the life of the underlying asset are capitalized. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are eliminated and any resulting gain or loss is reflected in the Company’s statements of operations and comprehensive loss. The treatment of costs to construct property and equipment depends on the nature of the costs and the stage of construction. Costs incurred in the project planning, design, construction and installation phases are capitalized as part of the cost of the asset. The Company stops capitalizing these costs when the asset is substantially complete and ready for its intended use. For manufacturing property and equipment, the Company also capitalizes the cost of validating these assets for the underlying manufacturing process. The Company completes the capitalization of validation costs when the asset is substantially complete and ready for its intended use. Costs capitalized include incremental labor and fringe benefits, and direct consultancy services. Other Assets Other assets include a $1.8 million non-controlling investment in a privately-held company that is accounted for under the cost method of accounting as of December 31, 2018 and 2017. The Company periodically evaluates the carrying value of the investment if significant adverse events or circumstances indicate an impairment in value. Business Combinations The Company records the fair value of the consideration transferred to acquire a business to the tangible assets and identifiable intangible assets acquired and liabilities assumed on the basis of their fair values at the date of acquisition. The Company assesses the fair value of assets, including intangible assets such as in‑process research and development (IPR&D), using a variety of methods including present-value models. Each asset is measured at fair value from the perspective of a market participant. The method used to estimate the fair values of IPR&D assets incorporates significant assumptions regarding the estimates a market participant would make in order to evaluate an asset, including a market participant’s assumptions regarding the probability of completing IPR&D projects, which would require obtaining regulatory approval for marketing of the associated drug candidate; a market participant’s estimates regarding the timing of and the expected costs to complete IPR&D projects; a market participant’s estimates of future cash flows from potential product sales; and the appropriate discount rates for a market participant. Transaction costs and restructuring costs associated with the transaction are expensed as incurred. The Company records contingent consideration resulting from a business combination at its fair value on the acquisition date. The Company determines the fair value of the contingent consideration based primarily on the (i) timing and probability of success of clinical events or regulatory approvals; (ii) timing and probability of success of meeting clinical and commercial milestones; and (iii) discount rates. The Company’s contingent consideration liabilities arose in connection with its acquisition of Kolltan. On a quarterly basis, the Company revalues these obligations and records increases or decreases in their fair value as an adjustment to operating earnings. Changes to contingent consideration obligations can result from adjustments to discount rates, accretion of the discount rates due to the passage of time, changes in the Company’s estimates of the likelihood or timing of achieving development or commercial milestones, changes in the probability of certain clinical events or changes in the assumed probability associated with regulatory approval. The assumptions related to determining the value of contingent consideration include a significant amount of judgment, and any changes in the underlying estimates could have a material impact on the amount of contingent consideration expense recorded in any given period. Intangible Assets IPR&D assets acquired in a business combination initially are recorded at fair value and accounted for as indefinite‑lived intangible assets. These assets are capitalized on the Company’s balance sheets until either the project underlying them is completed or the assets become impaired. If a project is completed, the carrying value of the related intangible asset is amortized over the remaining estimated life of the asset beginning in the period in which the project is completed. If a project becomes impaired or is abandoned, the carrying value of the related intangible asset is written down to its fair value and an impairment charge is taken in the period in which the impairment occurs. Each IPR&D asset is assessed for impairment at least annually or when impairment indicators are present. As a result of the discontinuation of the Glemba program, the Company concluded that the Glemba IPR&D asset was fully impaired, and a non-cash impairment charge of $11.8 million was recorded in the first quarter of 2018. The remaining IPR&D assets were assessed for impairment during 2018 and were determined not to be impaired. During the year ended December 31, 2017, the Company recorded a partial impairment charge of $13.0 million related to changes in projected development and regulatory timelines regarding the anti-KIT program. Intangible assets acquired in a business combination with a finite life are recorded at fair value and amortized over the greater of economic consumption or on a straight‑line basis over their estimated useful life. As a result of the discontinuation of the Glemba program, it was concluded that the Company’s finite-lived intangible asset was fully impaired and a non-cash impairment charge of $6.9 million was recorded in the first quarter of 2018. Goodwill The difference between the purchase price and the fair value of assets acquired and liabilities assumed in a business combination is allocated to goodwill. Goodwill is evaluated for impairment on an annual basis during the third quarter, or earlier if impairment indicators are present. The Company has the option to assess qualitative factors to determine if it is more likely than not that goodwill might be impaired and whether it is necessary to perform a quantitative single-step goodwill impairment test required under U.S. GAAP. As a result of the discontinuation of the Glemba program, the Company evaluated goodwill for potential impairment in the first quarter of 2018. It was determined that the goodwill asset was fully impaired and an impairment charge of $91.0 million was recorded . Impairment of Intangible and Long‑Lived Assets The Company evaluates the recoverability of its long‑lived assets, including property and equipment, and intangible assets when circumstances indicate that an event of impairment may have occurred. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the asset and its eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written‑down to their estimated fair values. Revenue Recognition Revenues are recognized when performance obligations under agreements or contracts are satisfied, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those services. The Company determines revenue recognition through the following steps: · Identification of the contract, or contracts, with a customer; · Identification of the performance obligations in the contract; · Determination of the transaction price; · Allocation of the transaction price to the performance obligations in the contract; and · Recognition of revenue when, or as, the Company satisfies a performance obligation. Revenue for the Company has historically been derived from biopharmaceutical product development agreements with collaborative partners for the research and development of therapeutic drug candidates. The terms of the agreements may include nonrefundable signing and licensing fees, funding for research, development and manufacturing, milestone payments and royalties on any product sales derived from collaborations. The Company assesses the multiple obligations typically within product development contracts to determine the distinct performance obligations and how to allocate the arrangement consideration to each distinct performance obligation. Under product development agreements, revenue is generally recognized using a cost-to-cost measure of progress. Revenue is recognized based on the costs incurred to date as a percentage of the total estimated costs to fulfill the contract. Incurred cost represents work performed, which corresponds with, and thereby best depicts, the transfer of control to the customer. Due to the nature of the work performed in these arrangements, the estimation of cost at completion is complex, subject to many variables, such as expected clinical trial costs, and requires significant judgements. Circumstances can arise that change original estimates of costs or progress toward completion. Any revisions to estimates are reflected in revenue on a cumulative catch-up basis in the period in which the change in circumstances became known. Revenue for the Company is also derived from manufacturing and research and development arrangements. The Company owns and operates a cGMP manufacturing facility in Fall River, Massachusetts, to produce drug substance for its current and planned early-stage clinical trials. In order to utilize excess capacity, the Company has, from time to time, entered into contract manufacturing and research and development arrangements in which services are provided on a time-and-material basis or at a negotiated fixed-price. Revenue from time-and-material contracts is generally recognized on an output basis as labor hours and/or direct expenses are incurred. Under fixed-price contracts, revenue is generally recognized on an output basis as progress is made toward completion of the performance obligations using surveys of performance completed to date. Contract Assets and Liabilities The Company classifies the right to consideration in exchange for products or services transferred to a client as either a receivable or a contract asset. A receivable is a right to consideration that is unconditional as compared to a contract asset which is a right to consideration that is conditional upon factors other than the passage of time. The Company’s contract liabilities result from arrangements where the Company has received payment in advance of performance under the contract. These amounts are included as deferred revenue within current portion of long-term liabilities on the condensed consolidated balance sheets. Research and Development Expenses Research and development costs, including internal and contract research costs, are expensed as incurred. Research and development expenses consist mainly of clinical trial costs, manufacturing of clinical material, toxicology and other preclinical studies, personnel costs, depreciation, license fees and funding of outside contracted research. Clinical trial expenses include expenses associated with clinical research organization, or CRO, services. Contract manufacturing expenses include expenses associated with contract manufacturing organization, or CMO, services. The invoicing from CROs and CMOs for services rendered can lag several months. The Company accrues the cost of services rendered in connection with CRO and CMO activities based on our estimate of costs incurred. The Company maintains regular communication with our CROs and CMOs to assess the reasonableness of its estimates. Differences between actual expenses and estimated expenses recorded have not been material and are adjusted for in the period in which they become known. Patent Costs Patent costs are expensed as incurred. Certain patent costs are reimbursed by the Company’s product development and licensing partners. Any reimbursed patent costs are recorded as product development and licensing agreement revenues in the Company’s financial statements. Stock‑Based Compensation The Company records stock-based compensation expense for all stock-based awards made to employees, directors and non-employees based on the estimated fair values of the stock-based awards expected to vest at the grant date and adjust, if necessary, to reflect actual forfeitures. Compensation expense for all stock-based awards is recognized using the straight-line method over the term of vesting or performance. Foreign Currency Translation Net unrealized gains and losses resulting from foreign currency translation are included in accumulated other comprehensive income. At December 31, 2018 and 2017, accumulated other comprehensive income includes a net unrealized gain related to foreign currency translation of $2.6 million. Income Taxes The Company uses the asset and liability method to account for income taxes, including the recognition of deferred tax assets and deferred tax liabilities for the anticipated future tax consequences attributable to differences between financial statement amounts and their respective tax basis. Quarterly, the Company reviews its deferred tax assets for recovery. A valuation allowance is established when the Company believes that it is more likely than not that its deferred tax assets will not be realized. Changes in valuation allowances from period to period are included in the Company’s tax provision in the period of change. The Company records uncertain tax positions in the financial statements only if it is more likely than not that the uncertain tax position will be sustained upon examination by the taxing authorities. The Company records interest and penalties related to uncertain tax positions in income tax expense. Comprehensive Loss Comprehensive loss is comprised of net loss and certain changes in stockholders’ equity that are excluded from net loss. The Company includes foreign currency translation adjustments and unrealized gains and losses on marketable securities in other comprehensive loss. The statements of operations and comprehensive loss reflect total comprehensive loss for the years ended December 31, 2018, 2017 and 2016. Net Loss Per Share Basic net loss per common share is based upon the weighted‑average number of common shares outstanding during the period, excluding restricted stock that has been issued but is not yet vested. Diluted net loss per common share is based upon the weighted‑average number of common shares outstanding during the period plus additional weighted-average potentially dilutive common shares outstanding during the period when the effect is dilutive. The potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive are as follows: Year Ended December 31, 2018 2017 2016 Stock options 866,132 723,747 681,248 Restricted stock 3,552 6,445 3,333 869,684 730,192 684,581 Newly - Adopted Accounting Pronouncements On January 1, 2018, the Company adopted the new U.S. GAAP standard “ Revenue from Contracts with Customers” using a modified retrospective application method, recognizing an immaterial cumulative-effect adjustment to accumulated deficit. The Company applied the new guidance to (i) contracts not completed as of the date of adoption and (ii) all new revenue contracts entered into after January 1, 2018. Refer to Note 12 “Revenue” for additional details on this adoption and the Company’s updated revenue accounting policy and disclosures. On January 1, 2018, the Company adopted a U.S. GAAP standard update “Classification of Certain Cash Receipts and Cash Payments” which clarifies the classification of certain cash receipts and payments in the statement of cash flows. The adoption of this new standard did not impact the Company’s consolidated financial statements. On July 1, 2018, the Company adopted a U.S. GAAP standard that aligns the accounting for share-based payment awards issued to employees and nonemployees. Under the new guidance, the existing employee guidance is applied to nonemployee share-based transactions. The adoption of this new standard did not have a material impact on the Company’s consolidated financial statements. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. In February 2016, the FASB issued a new U.S. GAAP accounting standard which requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. The Company will adopt the new guidance for its fiscal year beginning January 1, 2019 using the modified retrospective transition method, which requires the Company to apply the standard as of the effective date and does not require restatement of prior periods. The Company intends to elect the package of practical expedients, which will allow the Company to not reassess: (i) whether expired or existing contracts contain leases; (ii) lease classification for any expired or existing leases; and (iii) initial direct costs for any existing leases. The Company also plans to make a policy election not to record short term leases on the balance sheet. Adoption of this standard will not have a material impact on the Company’s Consolidated Statement of Operations and Comprehensive Loss or Statement of Cash Flow, however the Company expects to record a right-of-use asset of approximately $4.2 million and lease liability of approximately $4.7 million on its Consolidated Balance Sheet related to the Company’s operating leases. 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, 2020. We are currently evaluating the potential impact that this standard may have on the Company’s consolidated financial statements and related disclosures. In August 2018, the FASB issued amendments that modify certain disclosure requirements for fair value measurements. The amendments become effective, including interim periods, beginning January 1, 2020. Early adoption, of all the amendments or only the provisions that eliminate or modify the requirements, is permitted. The adoption of this new guidance is not expected to have a material impact on the Company’s consolidated financial statements and related disclosures. In November 2018, the FASB issued guidance to clarify the interaction between the accounting guidance for collaborative arrangements and revenue from contracts with customers. The amendments become effective, including interim periods, beginning January 1, 2020. Early adoption, including adoption in an interim period, is permitted. This guidance is required to be applied retrospectively as of the date of our adoption of the new revenue standard on January 1, 2018. We are currently evaluating the timing of our adoption and the expected impact this guidance could have on our consolidated financial statements and related disclosures.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2018
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income	(3) Accumulated Other Comprehensive Income The changes in accumulated other comprehensive income, which is reported as a component of stockholders’ equity, for the year ended December 31, 2018 are summarized below: Unrealized Gain (Loss) on Marketable Foreign Securities Currency Items Total (In thousands) Balance at December 31, 2017 $ (32) $ 2,596 $ 2,564 Other comprehensive gain 19 — 19 Balance at December 31, 2018 $ (13) $ 2,596 $ 2,583 No amounts were reclassified out of accumulated other comprehensive income during the years ended December 31, 2018, 2017 and 2016.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Measurements
Fair Value Measurements	(4) Fair Value Measurements The following tables set forth the Company’s financial assets and liabilities subject to fair value measurements: As of December 31, 2018 Level 1 Level 2 Level 3 (In thousands) Assets: Money market funds and cash equivalents $ 15,755 — $ 15,755 — Marketable securities 69,712 — 69,712 — $ 85,467 — $ 85,467 — Liabilities: Kolltan acquisition contingent consideration $ 13,779 — — $ 13,779 $ 13,779 — — $ 13,779 As of December 31, 2017 Level 1 Level 2 Level 3 (In thousands) Assets: Money market funds and cash equivalents $ 24,061 — $ 24,061 — Marketable securities 99,139 — 99,139 — $ 123,200 — $ 123,200 — Liabilities: Kolltan acquisition contingent consideration $ 43,400 — — $ 43,400 $ 43,400 — — $ 43,400 The Company’s financial assets consist mainly of cash and cash equivalents and marketable securities and are classified as Level 2 within the valuation hierarchy. The Company values its marketable securities utilizing independent pricing services which normally derive security prices from recently reported trades for identical or similar securities, making adjustments based on significant observable transactions. At each balance sheet date, observable market inputs may include trade information, broker or dealer quotes, bids, offers or a combination of these data sources. The following table reflects the activity for the Company’s contingent consideration liabilities measured at fair value using Level 3 inputs for the year ended December 31, 2018 (in thousands): Other Liabilities: Contingent Consideration Balance at December 31, 2017 $ 43,400 Fair value adjustments included in operating expenses (29,621) Balance at December 31, 2018 $ 13,779 The valuation technique During the year ended December 31, 2018, the Company recorded a $29.6 million gain on fair value remeasurement of contingent consideration, primarily due to discontinuation of the Glemba and CDX-014 programs, updated assumptions for the varlilumab program, and lower probability that milestones related to our anti-KIT program would be triggered by the Company’s current anti-KIT program development. The Company did not have any transfers of assets or liabilities between the fair value measurement classifications during the years ended December 31, 2018 and 2017.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2018
Marketable Securities
Marketable Securities	(5) Marketable Securities The following is a summary of marketable securities, classified as available-for-sale: Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value (In thousands) December 31, 2018 Marketable securities U.S. government and municipal obligations Maturing in one year or less $ 27,355 $ — $ (4) $ 27,351 Maturing after one year through three years — — — — Total U.S. government and municipal obligations $ 27,355 $ — $ (4) $ 27,351 Corporate debt securities Maturing in one year or less $ 42,370 $ — $ (9) $ 42,361 Maturing after one year through three years — — — — Total corporate debt securities $ 42,370 $ — $ (9) $ 42,361 Total marketable securities $ 69,725 $ — $ (13) $ 69,712 December 31, 2017 Marketable securities U.S. government and municipal obligations Maturing in one year or less $ 26,164 $ 3 $ (9) $ 26,158 Maturing after one year through three years — — — — Total U.S. government and municipal obligations $ 26,164 $ 3 $ (9) $ 26,158 Corporate debt securities Maturing in one year or less $ 73,007 $ 1 $ (27) $ 72,981 Maturing after one year through three years — — — — Total corporate debt securities $ 73,007 $ 1 $ (27) $ 72,981 Total marketable securities $ 99,171 $ 4 $ (36) $ 99,139 The Company holds investment grade marketable securities, and none were considered to be other‑than‑temporarily impaired as of December 31, 2018. Marketable securities include $0.1 million and $0.3 million in accrued interest at December 31, 2018 and December 31, 2017, respectively.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2018
Property and Equipment, Net
Property and Equipment, Net	(6) Property and Equipment, Net Property and Equipment, Net includes the following: December 31, December 31, 2018 2017 (In thousands) Laboratory Equipment $ 8,272 $ 7,770 Manufacturing Equipment 2,497 4,354 Office Furniture and Equipment 3,791 3,764 Leasehold Improvements 17,408 17,164 Construction in Progress 327 932 Total Property and Equipment 32,295 33,984 Less: Accumulated Depreciation and Amortization (26,184) (23,612) Property and Equipment, Net $ 6,111 $ 10,372 Depreciation and amortization expense related to property and equipment was $3.6 million, $4.4 million, and $3.1 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Intangible Assets and Goodwill

Intangible Assets and Goodwill	12 Months Ended
	Dec. 31, 2018
Intangible Assets and Goodwill
Intangible Assets and Goodwill	(7) Intangible Assets and Goodwill Intangible Assets, Net At December 31, 2018 and 2017, the Company recorded finite intangible assets of $0 and $7.1 million, respectively. Finite-lived intangible assets consisted solely of license rights amended under a 2009 agreement with Amgen Fremont related to developing and commercializing Glemba. As a result of the discontinuation of the Glemba program, the Company concluded that the finite-lived intangible asset was fully impaired and a non-cash impairment charge of $6.9 million was recorded in the first quarter of 2018. Amortization expense for finite intangible assets was $0.2 million, $0.9 million and $1.0 million for the years ended December 31, 2018, 2017 and 2016. At December 31, 2018 and 2017, the Company recorded indefinite-lived intangible assets of $48.7 million and $60.5 million, respectively. At December 31, 2018, 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 and the TAM program. CDX-3379 is in Phase 2 development. The anti-KIT and TAM programs are in preclinical development. As of December 31, 2018, no IPR&D asset had reached technological feasibility nor did any have alternative future uses. The Company performs an impairment test on IPR&D assets at least annually, or more frequently if events or changes in circumstances indicate that IPR&D assets may be impaired. As a result of the discontinuation of the Glemba program, the Company concluded that the Glemba IPR&D asset was fully impaired and a non-cash impairment charge of $11.8 million was recorded in the first quarter of 2018. 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. Goodwill At December 31, 2018 and 2017, the Company recorded goodwill of $0 and $91.0 million, respectively. The Company evaluated goodwill for potential impairment due to the discontinuation of the Glemba program. The carrying amount of the Company was compared to the Company’s fair value. The Company’s fair value assessment reflected a number of significant management assumptions and estimates including the Company’s probability forecasts for pipeline assets, income taxes, capital expenditures, market premium and changes in working capital requirements. Changes in these assumptions and/or discount rates could materially impact the Company’s conclusions. Through this assessment, it was determined that the carrying amount of the Company exceeded its fair value by over $91.0 million. As such, the full goodwill asset was considered impaired and a charge of $91.0 million was recorded during the first quarter of 2018.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2018
Accrued Expenses
Accrued Expenses	(8) Accrued Expenses Accrued expenses include the following: December 31, December 31, 2018 2017 (In thousands) Accrued Payroll and Employee Benefits $ 4,400 $ 6,348 Accrued Research and Development Contract Costs 1,766 11,399 Accrued Professional Fees 620 1,408 Other Accrued Expenses 221 300 $ 7,007 $ 19,455

Other Long-Term Liabilities

Other Long-Term Liabilities	12 Months Ended
	Dec. 31, 2018
Other Long-Term Liabilities
Other Long-Term Liabilities	(9) Other Long‑Term Liabilities Other long‑term liabilities include the following: December 31, December 31, 2018 2017 (In thousands) Net Deferred Tax Liabilities Related to IPR&D (Note 14) $ 3,007 $ 3,772 Deferred Income From Sale of Tax Benefits 4,218 6,756 Other 1,083 1,344 Contingent Milestones (Note 4) 13,779 43,400 Deferred Revenue 1,586 2,813 Total 23,673 58,085 Less Current Portion (4,526) (6,566) Long-Term Portion $ 19,147 $ 51,519 In November 2015, December 2014 and January 2014, the Company received approval from the New Jersey Economic Development Authority and agreed to sell New Jersey tax benefits of $9.8 million, $1.9 million and $1.1 million to an independent third party for $9.2 million, $1.8 million and $1.0 million, respectively. Under the agreement, the Company must maintain a base of operations in New Jersey for five years or the tax benefits must be paid back on a pro‑rata basis based on the number of years completed. During the years ended December 31, 2018, 2017 and 2016, the Company recorded $2.5 million, $2.7 million and $2.8 million to other income related to the sale of these tax benefits, respectively.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Stockholders' Equity
Stockholders' Equity	(10) Stockholders’ Equity Common Stock In December 2016, the Company filed a new shelf registration statement with the Securities and Exchange Commission to register for sale any combination of the types of securities described in the shelf registration statement up to a maximum aggregate offering price of $250 million. Such registration statement was declared effective on February 13, 2017. In May 2016, the Company entered into an agreement with Cantor Fitzgerald & Co. (“Cantor”) to allow the Company to issue and sell shares of its common stock having an aggregate offering price of up to $60.0 million from time to time through Cantor, acting as agent. In November 2017, the Company filed a prospectus supplement registering the offer and sale of shares of common stock of up to an additional $75.0 million under the agreement with Cantor. During the years ended December 31, 2018, 2017 and 2016, the Company issued 2,702,660, 1,181,524 and 220,253 shares of its common stock, respectively, under this controlled equity offering sales agreement with Cantor resulting in net proceeds to the Company of $29.0 million, $51.0 million and $13.9 million, respectively, after deducting commission and offering expenses. At December 31, 2018, the Company had $37.6 million remaining in aggregate gross offering price available under the Cantor agreement. From January 1, 2019 through February 28, 2019, the Company issued 478,785 shares of its common stock resulting in net proceeds to the Company of $2.3 million. Convertible Preferred Stock At December 31, 2018, the Company had authorized 3,000,000 shares of preferred stock all of which have been designated Class C Preferred Stock including 350,000 shares which have been designated Series C‑1 Junior Participating Cumulative Preferred Stock (the “Series C‑1 Preferred Stock”). No shares of Series C-1 Preferred Stock were outstanding at December 31, 2018 or 2017.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2018
Stock-Based Compensation
Stock-Based Compensation	(11) Stock‑Based Compensation The Company has the following stock-based compensation plans: the 2004 Employee Stock Purchase Plan (the “2004 ESPP Plan”) and the 2008 Stock Option and Incentive Plan (the “2008 Plan”). Employee Stock Purchase Plan At December 31, 2018, a total of 26,667 shares of common stock are reserved for issuance under the 2004 ESPP Plan. Under the 2004 ESPP Plan, each participating employee may purchase shares of common stock through payroll deductions at a purchase price equal to 85% of the lower of the fair market value of the common stock at either the beginning of the offering period or the applicable exercise date. During the years ended December 31, 2018, 2017 and 2016, the Company issued 9,524, 5,359 and 3,956 shares under the 2004 ESPP Plan, respectively. At December 31, 2018, 3,666 shares were available for issuance under the 2004 ESPP Plan. Employee Stock Option and Incentive Plan The 2008 Plan permits the granting of incentive stock options (intended to qualify as such under Section 422A of the Internal Revenue Code of 1986, as amended), non‑qualified stock options, stock appreciation rights, performance share units, restricted stock and other awards of restricted stock in lieu of cash bonuses to employees, consultants and non‑employee directors. At December 31, 2018, the 2008 Plan allowed for a maximum of 1,333,333 shares of common stock to be issued for grants of new awards until June 9, 2025 and grants of incentive stock options until April 16, 2025. The Company’s Board of Directors determines the term of each option, option price, and number of shares for which each option is granted and the rate at which each option vests. Options generally vest over a period not to exceed four years. The term of each option cannot exceed ten years (five years for options granted to holders of more than 10% of the voting stock of the Company), and the exercise price of stock options cannot be less than the fair market value of the common stock at the date of grant (110% of fair market value for incentive stock options granted to holders of more than 10% of the voting stock of the Company). Vesting of all employee and non‑employee director stock option awards may accelerate upon a change in control as defined in the 2008 Plan. A summary of stock option activity for the year ended December 31, 2018 is as follows: Weighted Weighted Average Average Exercise Remaining Price Contractual Shares Per Share Term (In Years) Options Outstanding at December 31, 2017 723,747 $ 141.00 6.1 Granted 338,517 $ 9.11 Exercised (6,967) $ 42.00 Canceled (189,165) $ 125.38 Options Outstanding at December 31, 2018 866,132 $ 93.70 7.1 Options Vested and Expected to Vest at December 31, 2018 846,352 $ 95.47 7.0 Options Exercisable at December 31, 2018 426,612 $ 162.83 5.1 Shares Available for Grant Under the 2008 Plan 356,913 The total intrinsic value of stock options exercised during the years ended December 31, 2018, 2017 and 2016 was $0.0 million, $0.0 million and $0.1 million, respectively. The weighted average grant‑date fair value of stock options granted during the years ended December 31, 2018, 2017 and 2016 was $6.60, $23.70 and $47.70, respectively. The total fair value of stock options vested during the years ended December 31, 2018, 2017 and 2016 was $8.0 million, $13.4 million and $17.0 million, respectively. The aggregate intrinsic value of stock options outstanding at December 31, 2018 was $0.0 million. The aggregate intrinsic value of stock options vested and expected to vest at December 31, 2018 was $0.0 million. As of December 31, 2018, total compensation cost related to non‑vested employee and non‑employee director stock options not yet recognized was approximately $6.8 million, net of estimated forfeitures, which is expected to be recognized as expense over a weighted average period of 2.6 years. Restricted Stock A summary of restricted stock activity under the 2008 Plan for the year ended December 31, 2018 is as follows: Weighted Average Grant Date Fair Value Shares (per share) Outstanding and unvested at December 31, 2017 6,445 $ 44.70 Granted — $ — Vested (2,449) $ 47.94 Canceled (444) $ 34.83 Outstanding and unvested at December 31, 2018 3,552 $ 43.84 Valuation and Expenses Information Stock‑based compensation expense for the years ended December 31, 2018, 2017 and 2016 was recorded as follows: 2018 2017 2016 (In thousands) Research and development $ 3,874 $ 6,693 $ 7,821 General and administrative 4,207 5,619 7,496 Total stock-based compensation expense $ 8,081 $ 12,312 $ 15,317 The fair values of employee and director stock options granted during the years ended December 31, 2018, 2017 and 2016 were valued using the Black‑Scholes option pricing model with the following assumptions: 2018 2017 2016 Expected stock price volatility 73 - 85% 75 - 77% 70 - 77% Expected option term 6.0 Years 6.0 Years 6.0 Years Risk-free interest rate 2.8 - 3.1% 2.0 - 2.3% 1.4 - 2.3% Expected dividend yield None None None The Company estimates expected term based on historical exercise patterns. The Company uses its historical stock price volatility consistent with the expected term of grant as the basis for its expected volatility assumption. The risk‑free interest rate is based upon the yield of U.S. Treasury securities consistent with the expected term of the option. The dividend yield assumption is based on the Company’s history of zero dividend payouts and expectation that no dividends will be paid in the foreseeable future.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2018
Revenue.
Revenue	(12) Revenue On January 1, 2018, the Company adopted a new revenue accounting standard, “ Revenue from Contracts with Customers” (ASC 606) . Upon adoption using the modified retrospective application, the Company recognized a $1.3 million decrease to accumulated deficit, a $0.8 million decrease in deferred revenue and $0.5 million increase in accounts receivable due to the cumulative impact of adopting ASC 606 . This impact was driven by the acceleration of revenue using a percentage-of-completion method of accounting under ASC 606 for an open contract that had previously been accounted for using the Contingency Adjusted Performance Model (“CAPM”) under previous guidance. Results for reporting periods beginning after January 1, 2018 are presented under ASC 606 while prior period amounts were not adjusted and continue to be reported in accordance with historic accounting under previous guidance. There was not a material impact to revenues as a result of applying ASC 606 for the year ended December 31, 2018, and there have not been significant changes to the Company’s business processes, systems or internal controls as a result of adopting the new standard. Revenue recognition remained largely unchanged under the new standard. Contract Assets and Liabilities At January 1, 2018 and December 31, 2018, the Company’s right to consideration under all contracts was considered unconditional, and as such, there were no recorded contract assets. Revenue recognized from contract liabilities as of January 1, 2018 during the year ended December 31, 2018 was $1.9 million. Revenue expected to be recognized in the future from contract liabilities as performance obligations are satisfied are not expected to be material. Product Development and Licensing Revenue The Company’s primary product development and licensing revenue is associated with a clinical collaboration agreement with BMS entered into in 2014 to evaluate the safety, tolerability and preliminary efficacy of varlilumab and Opdivo ® , BMS’s PD-1 immune checkpoint inhibitor, in a Phase 1/2 study. Under this agreement, BMS made an upfront payment to Celldex of $5.0 million and provides funding for 50% of the external costs incurred by the Company in connection with the clinical trial. The performance obligations under the collaboration agreement consist of intellectual property licenses and the performance of research and development services. The Company determined that the performance obligations were not separately identifiable and were not distinct (and did not have standalone value) due to the specialized nature of the services to be provided, the dependent relationship between the performance obligations and the Company’s proprietary technology that makes them uniquely qualified to perform the R&D services. Therefore, the Company concluded that the collaboration agreement has a single identified or combined performance obligation. As of December 31, 2018, deferred revenue related to the Company’s remaining performance obligation under this arrangement is not material. The Company recorded $3.3 million, $2.8 million and $2.1 million in revenue related to this agreement during the years ended December 31, 2018, 2017 and 2016, respectively. Contract and Grants Revenue In 2017, the Company entered into fixed-fee manufacturing and research and development arrangements with both the International AIDS Vaccine Initiative (IAVI) and Frontier Biotechnologies, Inc (Frontier). The Company recognized $3.0 million and $6.6 million in revenue under these agreements during the years ended December 31, 2018 and 2017, respectively. In 2013, the Company entered into an agreement, as amended, with Rockefeller University pursuant to which the Company performs manufacturing and research and development services for Rockefeller University. The Company recognized $2.6 million, $2.2 million and $2.7 million in revenue for labor hours and direct costs incurred related to the Rockefeller University agreement during years ended December 31, 2018, 2017 and 2016, respectively.

Collaboration Agreements

Collaboration Agreements	12 Months Ended
	Dec. 31, 2018
Collaboration Agreements
Collaboration Agreements	(13) Collaboration Agreements The Company has entered into license agreements whereby the Company has received licenses or options to license technology, specified patents or patent applications. The Company’s licensing and development collaboration agreements generally provide for royalty payments equal to specified percentages of product sales, annual license maintenance fees, continuing patent prosecution costs and potential future milestone payments to third parties upon the achievement of certain developmental, regulatory and/or commercial milestones. Nonrefundable license fee expense of $0.7 million, $0.7 million and $1.6 million was recorded to research and development expense for the years ended December 31, 2018, 2017 and 2016, respectively. Medarex, Inc. (Medarex), which was acquired by Bristol‑Myers Squibb Under a license agreement with Medarex, as amended, the Company acquired access to the UltiMab technology to develop and commercialize human antibodies to CD27, including varlilumab. The Company may be required to pay Medarex royalty payments in the low-to-mid single digits on any net product sales with respect to the development and commercialization of varlilumab until the later of (i) the expiration of the last to expire applicable patent and (ii) the tenth anniversary of the first commercial sale of such licensed product. University of Southampton, UK (Southampton) Under a license agreement with Southampton, the Company acquired the rights to develop human antibodies towards CD27, a potentially important target for immunotherapy of various cancers. The Company may be required to pay Southampton milestones of up to approximately $1.0 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low‑single digits on any net product sales with respect to development and commercialization of varlilumab. Amgen Inc. (Amgen) Under a license agreement with Amgen, the Company acquired the exclusive rights to CDX-301 and CD40 ligand, or CD40L. CDX-301 and CD40L are immune modulating molecules that increase the numbers and activity of immune cells that control immune responses. The Company may be required to pay Amgen milestones of up to $0.9 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low‑single digits on any net product sales with respect to development and commercialization of the technology licensed from Amgen, including CDX‑301. Yale University (Yale) Under a license agreement with Yale, the Company may be required to make a one-time payment to Yale of $3.0 million with respect to each therapeutic or prophylactic RTK royalty-bearing product, including CDX-3379, that achieves a specified commercial milestone. In addition, the Company may be required to pay a low single-digit royalty on annual worldwide net sales of each RTK royalty-bearing product, including CDX-3379. MedImmune, LLC (MedImmune) Under a license agreement with MedImmune, the Company acquired exclusive rights to specified patent rights and know-how that are controlled by MedImmune and relate to the research, development, manufacture and commercialization of CDX-3379. The Company may be required to pay Medimmune up to $45.0 million upon obtaining specified regulatory and development milestones in the first indication of CDX-3379. In addition, the Company may be required to pay MedImmune one-time milestone payments of up to $125.0 million if specified annual net sale thresholds are met related to the first indication of CDX-3379. The Company may also be required to pay MedImmune a tiered royalty on annual net sales of CDX-3379 at rates ranging from high single-digit to low teens percentages. The Company may also be required to pay specified royalties on annual net sales of CDX-3379 at a rate in the low single digits to certain other third parties from whom MedImmune licensed certain intellectual property.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Taxes
Income Taxes	(14) Income Taxes The components of income tax benefit (provision) are as follows: Year Ended December 31, 2018 2017 2016 (In thousands) Income Tax Benefit (Provision): Federal $ 22,255 $ 57,547 $ 45,518 State 6,406 (2,479) 7,268 Foreign 913 2,448 1,124 Income Tax Rate Change — (99,528) — 29,574 (42,012) 53,910 Deferred Tax Valuation Allowance (28,809) 66,294 (53,910) $ 765 $ 24,282 $ — A reconciliation between the amount of reported income tax and the amount computed using the U.S. Statutory rate is as follows: 2018 2017 2016 (In thousands) Pre-Tax Loss $ (151,949) $ (117,313) $ (128,530) Loss at Statutory Rates (31,909) (39,887) (43,700) Difference in Foreign Tax Rates — 326 150 Research and Development Credits (2,056) (2,847) (5,203) State Taxes (6,406) (6,283) (7,268) Income Tax Rate Change — 99,528 — Other (1,175) (321) 2,111 Milestone Abandonment (6,220) — — Intangible Impairment 19,105 — — Recognition of APIC NOLs — (5,729) — Impact of Pass-through Entities (913) (2,775) — Change in Valuation Allowance 28,809 (66,294) 53,910 Income Tax (Benefit) Provision $ (765) $ (24,282) $ — Deferred tax assets and liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using future expected enacted rates. The principal components of the deferred tax assets and liabilities at December 31, 2018 and 2017, respectively, are as follows: December 31, December 31, 2018 2017 (In thousands) Gross Deferred Tax Assets Net Operating Loss Carryforwards $ 168,239 $ 146,228 Foreign Net Operating Loss Carryforwards 4,485 3,572 Tax Credit Carryforwards 39,761 36,458 Deferred Research and Development Expenses 76,555 79,272 Stock-based Compensation 11,977 10,718 Fixed Assets 1,761 1,305 Deferred Revenue 13 686 Accrued Expenses and Other 183 316 302,974 278,555 Gross Deferred Tax Liabilities Other Acquired Intangibles 120 (1,792) IPR&D Intangibles (12,748) (15,992) Total Deferred Tax Assets and Liabilities 290,346 260,771 Valuation Allowance (293,353) (264,543) Net Deferred Tax Liability $ (3,007) $ (3,772) The Company has evaluated the positive and negative evidence bearing upon the realizability of its net deferred tax assets and considered its history of losses, ultimately concluding that it is “more likely than not” that the Company will not recognize the benefits of federal, state and foreign deferred tax assets and, as such, has maintained a full valuation allowance on its deferred tax assets. During year ended December 31, 2017, the Company’s gross deferred tax assets and corresponding valuation allowance each increased by $17.7 million. This was a one-time increase due to the adoption of a new accounting standard removing the requirement to recognize excess tax benefits from the exercise of stock options in additional paid-in-capital when realized. On December 22, 2017, the Tax Cuts and Jobs Act (“TCJA”) was enacted, leading to significant changes to U.S. tax law. Among other provisions, the TCJA lowered the U.S. federal corporate income tax rate from 35% to 21%, limited the deduction for net operating losses to 80% of taxable income while providing that net operating loss carryovers for years after 2017 will not expire, imposed a mandatory one-time transition tax on previously deferred foreign earnings and eliminated or reduced certain income tax deductions. As a result of the TCJA, the Company revalued its deferred tax liabilities at the new federal rate of 21%, resulting in a $6.9 million decrease and a corresponding income tax benefit. The Company also scheduled out reversals of its deferred tax assets and liabilities, determining that their reversal would create future indefinite‑lived net operating losses under the TCJA. As such, the valuation allowance was reduced relating to the remaining indefinite‑lived federal deferred tax liabilities balance, leading to an additional income tax benefit of $12.2 million. The net deferred tax liability of $3.0 million and $3.8 million at December 31, 2018 and 2017, respectively, relates to the temporary differences associated with the IPR&D intangible assets acquired in previous business combinations and are not deductible for tax purposes. The Company recorded an income tax benefit of $0.8 million during the year ended December 31, 2018 due to a decrease in deferred tax liabilities resulting from the partial impairment of the anti-KIT program. As of December 31, 2018, the Company had federal and state net operating loss carryforwards of $636.8 million and $532.4 million, respectively, which may be available to offset certain future income tax liabilities and begin to expire in 2019 and 2028, respectively. Of the federal net operating loss carryforwards of $636.8 million, approximately $75 million are from 2018 and have no expiration date. As of December 31, 2018, the Company also had federal and state research and development tax credit carryforwards of $31.0 million and $11.1 million, respectively, which may be available to offset future income tax liabilities and begin to expire in 2018 and 2017, respectively. Utilization of the net operating loss carryforwards and research and credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, or Section 382, due to ownership changes that occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three‑year period. The Company has estimated the amounts of net operating loss and research and development tax credit carryforwards which will expire unutilized as a result of its estimated annual limitations under Section 382 and has excluded those amounts from the carryforward amounts disclosed above and in the deferred tax assets and liabilities table included in this footnote. The Company has concluded Section 382 studies through 2015 for Celldex generated NOLs. The Company incurred a foreign pre-tax loss of $3.0 million and $8.2 million during the years ended December 31, 2018 and 2017, respectively. Beginning with the 2016 tax returns, the Company elected to classify the Australian entity as a disregarded entity for income tax purposes. The foreign pre-tax losses have been included with the Federal net operating loss carryforwards. As of December 31, 2018 and 2017, the Company did not have any unrecognized tax benefits. Massachusetts, New Jersey, New York, Connecticut and Australia are the jurisdictions in which the Company primarily operates or has operated and has income tax nexus. The Company is not currently under examination by these or any other jurisdictions for any tax year. Generally, in U.S. federal and state taxing jurisdictions, all years which generated net operating losses and/or tax credit carryforwards remain subject to examination to the extent those carryforwards are utilized in a subsequent period.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies
Commitments and Contingencies	(15) Commitments and Contingencies The Company has facility and equipment leases that expire at various dates through 2020. Certain of these facility leases contain renewal options, early termination provisions, and provisions that escalate the base rent payments and require the Company to pay common area maintenance costs (“CAM”) during the lease term. The following obligations for base rent and CAM costs under facility and other non‑cancelable operating leases as of December 31, 2018 do not include the exercise of renewal terms or early termination provisions (in thousands): 2019 $ 4,648 2020 3,140 2021 — 2022 — 2023 — Thereafter — Total minimum lease payments $ 7,788 The Company’s total rent and CAM expense for all facility leases was $4.0 million, $4.1 million and $4.8 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Retirement Savings Plan

Retirement Savings Plan	12 Months Ended
	Dec. 31, 2018
Retirement Savings Plan
Retirement Savings Plan	(16) Retirement Savings Plan The Company maintains a 401(k) Plan which is available to substantially all employees. Under the terms of the 401(k) Plan, participants may elect to contribute up to 60% of their compensation or the statutory prescribed limits. The Company may make 50% matching contributions on up to 4% of a participant’s annual salary. Benefit expense for the 401(k) Plan was $0.4 million, $0.5 million and $0.4 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Kolltan Acquisition

Kolltan Acquisition	12 Months Ended
	Dec. 31, 2018
Kolltan Acquisition
Kolltan Acquisition	(17) Kolltan Acquisition On November 29, 2016, the Company acquired all of the share and debt interests of Kolltan Pharmaceuticals, Inc. (“Kolltan”), a clinical-stage biopharmaceutical company, in exchange for 1,217,200 shares of the Company’s common stock plus contingent consideration in the form of development and approval milestones. As of December 31, 2018, the Company may be required to pay future consideration of up to $127.5 million that is contingent upon the achievement of specified development, regulatory approvals or sales-based milestone events. The Company completed this acquisition in order to gain access to Kolltan’s antibody-based drug development programs targeting receptor tyrosine kinases (RTKs) for the treatment of cancer and other diseases with significant unmet needs. Purchase Price The purchase price for Kolltan was calculated based on the closing price of the Company’s common stock of $60.30 per share on November 29, 2016. The Company also recorded a liability of $44.2 million which represented the initial fair value of the contingent consideration. This fair value measurement used significant unobservable inputs representing a Level 3 measurement more fully described in Note 4, Fair Value Measurements to these consolidated financial statements. Subsequent changes to the fair value of the contingent consideration will be recognized as adjustments to operating earnings. The acquisition was accounted for using the acquisition method of accounting which requires all assets acquired and liabilities assumed recognized at their acquisition-date fair values. The total consideration transferred consisted of the following (in thousands): Fair value of common stock issued for upfront payment $ 73,397 Fair value of contingent consideration 44,200 Kolltan transaction expenses paid in cash by the Company 3,768 Total consideration transferred $ 121,365 Allocations of Assets and Liabilities The purchase price allocation was finalized in the fourth quarter of 2017 with no adjustments made to the initial purchase price allocation. The following table summarizes the fair values of the assets acquired and liabilities assumed as of November 29, 2016 (in thousands): Cash and cash equivalents $ 8,160 Other current and long-term assets 799 Property and equipment, net 2,072 In-process research and development (IPR&D) 61,690 Goodwill 82,011 Deferred tax liabilities, net (23,393) Other assumed liabilities (9,974) Total $ 121,365 IPR&D primarily represents the initial estimated fair value of $40.0 million, $3.5 million and $18.0 million for the anti-KIT program, CDX-3379 and TAM programs, respectively, using probability adjusted discounted cash flow analyses. The expected future net cash flows for the anti-KIT program, CDX-3379 and TAM programs were based on the expectation that a Biologics License Application (“BLA”) would be filed with the FDA no earlier than the end of 2023, 2024 and 2028, respectively, with an expected commercial launch as promptly as practicable after necessary regulatory approvals are received. The estimated development costs included in the expected future net cash flows were approximately $132 million combined. The deferred tax liability, net of $23.4 million primarily relates to the temporary differences associated with the IPR&D intangible assets, which are not deductible for tax purposes. The excess of purchase price over the fair value amounts assigned to the identifiable assets acquired and liabilities assumed represents the goodwill amount resulting from the acquisition. The value of the goodwill can be attributable to the synergies related to the combined antibody-based platform and a deferred tax liability related to acquired IPR&D intangible assets. None of the goodwill is expected to be deductible for income tax purposes. Acquisition-Related Expenses, Including Severance The Company incurred $0.7 million in acquisition-related expenses in the consolidated statements of operations for the year ended December 31, 2016. From the acquisition date through December 31, 2016, the consolidated statements of operations also include $2.4 and $0.7 million in Kolltan related severance expense within general and administrative and research and development expenses, respectively. Pro Forma Financial Information The operating results of Kolltan and pro forma adjustments including severance expense and transaction expenses of $3.1 million and $0.7 million, respectively, have been included in the accompanying consolidated financial statements from November 29, 2016 to December 31, 2016. Kolltan had no revenues from November 29, 2016 through December 31, 2016. The following unaudited pro forma financial summary is presented as if the operations of the Company and Kolltan were combined as of January 1, 2015. The unaudited pro forma combined results are not necessarily indicative of the actual results that would have occurred had the acquisition been consummated at that date or of the future operations of the combined entities. Unaudited Years Ended December 31, 2016 (In thousands) Revenue $ 6,786 Net loss $ (146,905)

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Data (Unaudited)
Selected Quarterly Financial Data (Unaudited)	(18) Selected Quarterly Financial Data (Unaudited) 2018 Q1 2018 Q2 2018 Q3 2018 Q4 2018 (In thousands, except per share amounts) Total revenue $ 4,068 $ 2,763 $ 941 $ 1,764 Net loss (118,132) (16,407) (7,243) (9,402) Basic and diluted net loss per common share (12.61) (1.67) (0.66) (0.81) 2017 Q1 2017 Q2 2017 Q3 2017 Q4 2017 (In thousands, except per share amounts) Total revenue $ 1,534 $ 3,829 $ 3,924 $ 3,456 Net loss (34,261) (28,566) (26,363) (3,841) Basic and diluted net loss per common share (4.19) (3.42) (3.05) (0.42)

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The balance sheets and statements of operations and comprehensive loss, stockholders’ equity, and cash flows, are consolidated for the years ended December 31, 2018 and 2017. These consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company operates in one segment, which is the business of development, manufacturing and commercialization of novel therapeutics for human health care.
Use of Estimates	Use of Estimates The preparation of the financial statements in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP) requires management to make estimates and use assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the dates of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with a maturity date of 90 days or less at the date of purchase to be cash equivalents. Cash equivalents consist principally of money market funds and debt securities.
Marketable Securities	Marketable Securities The Company invests its excess cash balances in marketable securities, including municipal bond securities, U.S. government agency securities, and highly rated corporate bonds. The Company classifies all of its marketable securities as current assets on the balance sheets because they are available-for-sale and available to fund current operations. Marketable securities are stated at fair value with unrealized gains and losses included as a component of accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity, until such gains and losses are realized. If a decline in the fair value is considered other-than-temporary, based on available evidence, the unrealized loss is reclassified from accumulated other comprehensive income (loss) to the statements of operations. Realized gains and losses are determined on the specific identification method and are included in investment and other income, net.
Concentration of Credit Risk and of Significant Customers and Suppliers	Concentration of Credit Risk and of Significant Customers and Suppliers Financial instruments that potentially subject the Company to concentrations of credit risk primarily consist of cash, cash equivalents, marketable securities and accounts receivable. The Company invests its cash, cash equivalents and marketable securities in debt instruments and interest-bearing accounts at major financial institutions in excess of insured limits. The Company mitigates credit risk by limiting the investment type and maturity to securities that preserve capital, maintain liquidity and have a high credit quality. The Company has not historically experienced credit losses from its accounts receivable and therefore has not established an allowance for doubtful accounts. Combined revenue from BMS, Rockefeller and International AIDS Vaccine Initiative represented 86% of total Company revenue for the year ended December 31, 2018 and 77% of total Company revenue for the year ended December 31, 2017. Combined revenue from Rockefeller and BMS represented 71% of total Company revenue for the year ended December 31, 2016. The Company relies on contract manufacturing organizations (CMO) to manufacture drug substance and drug product as well as for future commercial supplies. The Company also relies on CMOs for supply of raw materials as well as filling, packaging, storing and shipping our drug products. The Company relies on third‑party collaborators to develop companion diagnostic tests.
Fair Value Measurements	Fair Value Measurements The Company has certain assets and liabilities that are measured at fair value in the financial statements. The Company seeks to maximize the use of observable inputs (market data obtained from sources independent from the Company) and to minimize the use of unobservable inputs (the Company’s assumptions about how market participants would price assets and liabilities) when measuring the fair value of its assets and liabilities. These assets and liabilities are classified into one of three levels of the following fair value hierarchy as defined by U.S. GAAP: Level 1: Observable inputs such as quoted prices in active markets for identical assets or liabilities. An active market for an asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2: Observable inputs other than Level 1 prices, such as quoted prices in active markets for similar assets or liabilities and quoted prices for identical assets or liabilities in markets that are not active. Level 3: Unobservable inputs based on the Company’s assessment of the assumptions that market participants would use in pricing the asset or liability.
Property and Equipment	Property and Equipment Property and equipment is stated at cost and depreciated over the estimated useful lives of the related assets using the straight‑line method. Laboratory equipment and office furniture and equipment are depreciated over five years, and computer equipment is depreciated over three years. Manufacturing equipment is amortized over seven to ten years. Leasehold improvements are amortized over the shorter of the estimated useful life or the non‑cancelable term of the related lease, including any renewals that are reasonably assured of occurring. Property and equipment under construction is classified as construction in progress and is depreciated or amortized only after the asset is placed in service. Expenditures for maintenance and repairs are charged to expense whereas the costs of significant improvements which extend the life of the underlying asset are capitalized. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are eliminated and any resulting gain or loss is reflected in the Company’s statements of operations and comprehensive loss. The treatment of costs to construct property and equipment depends on the nature of the costs and the stage of construction. Costs incurred in the project planning, design, construction and installation phases are capitalized as part of the cost of the asset. The Company stops capitalizing these costs when the asset is substantially complete and ready for its intended use. For manufacturing property and equipment, the Company also capitalizes the cost of validating these assets for the underlying manufacturing process. The Company completes the capitalization of validation costs when the asset is substantially complete and ready for its intended use. Costs capitalized include incremental labor and fringe benefits, and direct consultancy services.
Other Assets	Other Assets Other assets include a $1.8 million non-controlling investment in a privately-held company that is accounted for under the cost method of accounting as of December 31, 2018 and 2017. The Company periodically evaluates the carrying value of the investment if significant adverse events or circumstances indicate an impairment in value.
Business Combinations	Business Combinations The Company records the fair value of the consideration transferred to acquire a business to the tangible assets and identifiable intangible assets acquired and liabilities assumed on the basis of their fair values at the date of acquisition. The Company assesses the fair value of assets, including intangible assets such as in‑process research and development (IPR&D), using a variety of methods including present-value models. Each asset is measured at fair value from the perspective of a market participant. The method used to estimate the fair values of IPR&D assets incorporates significant assumptions regarding the estimates a market participant would make in order to evaluate an asset, including a market participant’s assumptions regarding the probability of completing IPR&D projects, which would require obtaining regulatory approval for marketing of the associated drug candidate; a market participant’s estimates regarding the timing of and the expected costs to complete IPR&D projects; a market participant’s estimates of future cash flows from potential product sales; and the appropriate discount rates for a market participant. Transaction costs and restructuring costs associated with the transaction are expensed as incurred. The Company records contingent consideration resulting from a business combination at its fair value on the acquisition date. The Company determines the fair value of the contingent consideration based primarily on the (i) timing and probability of success of clinical events or regulatory approvals; (ii) timing and probability of success of meeting clinical and commercial milestones; and (iii) discount rates. The Company’s contingent consideration liabilities arose in connection with its acquisition of Kolltan. On a quarterly basis, the Company revalues these obligations and records increases or decreases in their fair value as an adjustment to operating earnings. Changes to contingent consideration obligations can result from adjustments to discount rates, accretion of the discount rates due to the passage of time, changes in the Company’s estimates of the likelihood or timing of achieving development or commercial milestones, changes in the probability of certain clinical events or changes in the assumed probability associated with regulatory approval. The assumptions related to determining the value of contingent consideration include a significant amount of judgment, and any changes in the underlying estimates could have a material impact on the amount of contingent consideration expense recorded in any given period.
Intangible Assets	Intangible Assets IPR&D assets acquired in a business combination initially are recorded at fair value and accounted for as indefinite‑lived intangible assets. These assets are capitalized on the Company’s balance sheets until either the project underlying them is completed or the assets become impaired. If a project is completed, the carrying value of the related intangible asset is amortized over the remaining estimated life of the asset beginning in the period in which the project is completed. If a project becomes impaired or is abandoned, the carrying value of the related intangible asset is written down to its fair value and an impairment charge is taken in the period in which the impairment occurs. Each IPR&D asset is assessed for impairment at least annually or when impairment indicators are present. As a result of the discontinuation of the Glemba program, the Company concluded that the Glemba IPR&D asset was fully impaired, and a non-cash impairment charge of $11.8 million was recorded in the first quarter of 2018. The remaining IPR&D assets were assessed for impairment during 2018 and were determined not to be impaired. During the year ended December 31, 2017, the Company recorded a partial impairment charge of $13.0 million related to changes in projected development and regulatory timelines regarding the anti-KIT program. Intangible assets acquired in a business combination with a finite life are recorded at fair value and amortized over the greater of economic consumption or on a straight‑line basis over their estimated useful life. As a result of the discontinuation of the Glemba program, it was concluded that the Company’s finite-lived intangible asset was fully impaired and a non-cash impairment charge of $6.9 million was recorded in the first quarter of 2018.
Goodwill	Goodwill The difference between the purchase price and the fair value of assets acquired and liabilities assumed in a business combination is allocated to goodwill. Goodwill is evaluated for impairment on an annual basis during the third quarter, or earlier if impairment indicators are present. The Company has the option to assess qualitative factors to determine if it is more likely than not that goodwill might be impaired and whether it is necessary to perform a quantitative single-step goodwill impairment test required under U.S. GAAP. As a result of the discontinuation of the Glemba program, the Company evaluated goodwill for potential impairment in the first quarter of 2018. It was determined that the goodwill asset was fully impaired and an impairment charge of $91.0 million was recorded .
Impairment of Intangible and Long-Lived Assets	Impairment of Intangible and Long‑Lived Assets The Company evaluates the recoverability of its long‑lived assets, including property and equipment, and intangible assets when circumstances indicate that an event of impairment may have occurred. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the asset and its eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written‑down to their estimated fair values.
Revenue Recognition	Revenue Recognition Revenues are recognized when performance obligations under agreements or contracts are satisfied, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those services. The Company determines revenue recognition through the following steps: · Identification of the contract, or contracts, with a customer; · Identification of the performance obligations in the contract; · Determination of the transaction price; · Allocation of the transaction price to the performance obligations in the contract; and · Recognition of revenue when, or as, the Company satisfies a performance obligation. Revenue for the Company has historically been derived from biopharmaceutical product development agreements with collaborative partners for the research and development of therapeutic drug candidates. The terms of the agreements may include nonrefundable signing and licensing fees, funding for research, development and manufacturing, milestone payments and royalties on any product sales derived from collaborations. The Company assesses the multiple obligations typically within product development contracts to determine the distinct performance obligations and how to allocate the arrangement consideration to each distinct performance obligation. Under product development agreements, revenue is generally recognized using a cost-to-cost measure of progress. Revenue is recognized based on the costs incurred to date as a percentage of the total estimated costs to fulfill the contract. Incurred cost represents work performed, which corresponds with, and thereby best depicts, the transfer of control to the customer. Due to the nature of the work performed in these arrangements, the estimation of cost at completion is complex, subject to many variables, such as expected clinical trial costs, and requires significant judgements. Circumstances can arise that change original estimates of costs or progress toward completion. Any revisions to estimates are reflected in revenue on a cumulative catch-up basis in the period in which the change in circumstances became known. Revenue for the Company is also derived from manufacturing and research and development arrangements. The Company owns and operates a cGMP manufacturing facility in Fall River, Massachusetts, to produce drug substance for its current and planned early-stage clinical trials. In order to utilize excess capacity, the Company has, from time to time, entered into contract manufacturing and research and development arrangements in which services are provided on a time-and-material basis or at a negotiated fixed-price. Revenue from time-and-material contracts is generally recognized on an output basis as labor hours and/or direct expenses are incurred. Under fixed-price contracts, revenue is generally recognized on an output basis as progress is made toward completion of the performance obligations using surveys of performance completed to date.
Contract Assets and Liabilities	Contract Assets and Liabilities The Company classifies the right to consideration in exchange for products or services transferred to a client as either a receivable or a contract asset. A receivable is a right to consideration that is unconditional as compared to a contract asset which is a right to consideration that is conditional upon factors other than the passage of time. The Company’s contract liabilities result from arrangements where the Company has received payment in advance of performance under the contract. These amounts are included as deferred revenue within current portion of long-term liabilities on the condensed consolidated balance sheets.
Research and Development Expenses	Research and Development Expenses Research and development costs, including internal and contract research costs, are expensed as incurred. Research and development expenses consist mainly of clinical trial costs, manufacturing of clinical material, toxicology and other preclinical studies, personnel costs, depreciation, license fees and funding of outside contracted research. Clinical trial expenses include expenses associated with clinical research organization, or CRO, services. Contract manufacturing expenses include expenses associated with contract manufacturing organization, or CMO, services. The invoicing from CROs and CMOs for services rendered can lag several months. The Company accrues the cost of services rendered in connection with CRO and CMO activities based on our estimate of costs incurred. The Company maintains regular communication with our CROs and CMOs to assess the reasonableness of its estimates. Differences between actual expenses and estimated expenses recorded have not been material and are adjusted for in the period in which they become known.
Patent Costs	Patent Costs Patent costs are expensed as incurred. Certain patent costs are reimbursed by the Company’s product development and licensing partners. Any reimbursed patent costs are recorded as product development and licensing agreement revenues in the Company’s financial statements.
Stock-Based Compensation	Stock‑Based Compensation The Company records stock-based compensation expense for all stock-based awards made to employees, directors and non-employees based on the estimated fair values of the stock-based awards expected to vest at the grant date and adjust, if necessary, to reflect actual forfeitures. Compensation expense for all stock-based awards is recognized using the straight-line method over the term of vesting or performance.
Foreign Currency Translation	Foreign Currency Translation Net unrealized gains and losses resulting from foreign currency translation are included in accumulated other comprehensive income. At December 31, 2018 and 2017, accumulated other comprehensive income includes a net unrealized gain related to foreign currency translation of $2.6 million.
Income Taxes	Income Taxes The Company uses the asset and liability method to account for income taxes, including the recognition of deferred tax assets and deferred tax liabilities for the anticipated future tax consequences attributable to differences between financial statement amounts and their respective tax basis. Quarterly, the Company reviews its deferred tax assets for recovery. A valuation allowance is established when the Company believes that it is more likely than not that its deferred tax assets will not be realized. Changes in valuation allowances from period to period are included in the Company’s tax provision in the period of change. The Company records uncertain tax positions in the financial statements only if it is more likely than not that the uncertain tax position will be sustained upon examination by the taxing authorities. The Company records interest and penalties related to uncertain tax positions in income tax expense.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is comprised of net loss and certain changes in stockholders’ equity that are excluded from net loss. The Company includes foreign currency translation adjustments and unrealized gains and losses on marketable securities in other comprehensive loss. The statements of operations and comprehensive loss reflect total comprehensive loss for the years ended December 31, 2018, 2017 and 2016.
Net Loss Per Share	Net Loss Per Share Basic net loss per common share is based upon the weighted‑average number of common shares outstanding during the period, excluding restricted stock that has been issued but is not yet vested. Diluted net loss per common share is based upon the weighted‑average number of common shares outstanding during the period plus additional weighted-average potentially dilutive common shares outstanding during the period when the effect is dilutive. The potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive are as follows: Year Ended December 31, 2018 2017 2016 Stock options 866,132 723,747 681,248 Restricted stock 3,552 6,445 3,333 869,684 730,192 684,581
Newly-Adopted Accounting Pronouncements	Newly - Adopted Accounting Pronouncements On January 1, 2018, the Company adopted the new U.S. GAAP standard “ Revenue from Contracts with Customers” using a modified retrospective application method, recognizing an immaterial cumulative-effect adjustment to accumulated deficit. The Company applied the new guidance to (i) contracts not completed as of the date of adoption and (ii) all new revenue contracts entered into after January 1, 2018. Refer to Note 12 “Revenue” for additional details on this adoption and the Company’s updated revenue accounting policy and disclosures. On January 1, 2018, the Company adopted a U.S. GAAP standard update “Classification of Certain Cash Receipts and Cash Payments” which clarifies the classification of certain cash receipts and payments in the statement of cash flows. The adoption of this new standard did not impact the Company’s consolidated financial statements. On July 1, 2018, the Company adopted a U.S. GAAP standard that aligns the accounting for share-based payment awards issued to employees and nonemployees. Under the new guidance, the existing employee guidance is applied to nonemployee share-based transactions. The adoption of this new standard did not have a material impact on the Company’s consolidated financial statements.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. In February 2016, the FASB issued a new U.S. GAAP accounting standard which requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. The Company will adopt the new guidance for its fiscal year beginning January 1, 2019 using the modified retrospective transition method, which requires the Company to apply the standard as of the effective date and does not require restatement of prior periods. The Company intends to elect the package of practical expedients, which will allow the Company to not reassess: (i) whether expired or existing contracts contain leases; (ii) lease classification for any expired or existing leases; and (iii) initial direct costs for any existing leases. The Company also plans to make a policy election not to record short term leases on the balance sheet. Adoption of this standard will not have a material impact on the Company’s Consolidated Statement of Operations and Comprehensive Loss or Statement of Cash Flow, however the Company expects to record a right-of-use asset of approximately $4.2 million and lease liability of approximately $4.7 million on its Consolidated Balance Sheet related to the Company’s operating leases. 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, 2020. We are currently evaluating the potential impact that this standard may have on the Company’s consolidated financial statements and related disclosures. In August 2018, the FASB issued amendments that modify certain disclosure requirements for fair value measurements. The amendments become effective, including interim periods, beginning January 1, 2020. Early adoption, of all the amendments or only the provisions that eliminate or modify the requirements, is permitted. The adoption of this new guidance is not expected to have a material impact on the Company’s consolidated financial statements and related disclosures. In November 2018, the FASB issued guidance to clarify the interaction between the accounting guidance for collaborative arrangements and revenue from contracts with customers. The amendments become effective, including interim periods, beginning January 1, 2020. Early adoption, including adoption in an interim period, is permitted. This guidance is required to be applied retrospectively as of the date of our adoption of the new revenue standard on January 1, 2018. We are currently evaluating the timing of our adoption and the expected impact this guidance could have on our consolidated financial statements and related disclosures

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Summary of Significant Accounting Policies
Schedule of potentially dilutive common shares that have not been included in the net loss per common share calculations because the effect would have been anti-dilutive	Year Ended December 31, 2018 2017 2016 Stock options 866,132 723,747 681,248 Restricted stock 3,552 6,445 3,333 869,684 730,192 684,581

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2017 $ (32) $ 2,596 $ 2,564 Other comprehensive gain 19 — 19 Balance at December 31, 2018 $ (13) $ 2,596 $ 2,583

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Measurements
Schedule of financial assets and liabilities subject to fair value measurements	As of December 31, 2018 Level 1 Level 2 Level 3 (In thousands) Assets: Money market funds and cash equivalents $ 15,755 — $ 15,755 — Marketable securities 69,712 — 69,712 — $ 85,467 — $ 85,467 — Liabilities: Kolltan acquisition contingent consideration $ 13,779 — — $ 13,779 $ 13,779 — — $ 13,779 As of December 31, 2017 Level 1 Level 2 Level 3 (In thousands) Assets: Money market funds and cash equivalents $ 24,061 — $ 24,061 — Marketable securities 99,139 — 99,139 — $ 123,200 — $ 123,200 — Liabilities: Kolltan acquisition contingent consideration $ 43,400 — — $ 43,400 $ 43,400 — — $ 43,400
Schedule of the Company's contingent consideration liabilities measured at fair value using Level 3 inputs	The following table reflects the activity for the Company’s contingent consideration liabilities measured at fair value using Level 3 inputs for the year ended December 31, 2018 (in thousands): Other Liabilities: Contingent Consideration Balance at December 31, 2017 $ 43,400 Fair value adjustments included in operating expenses (29,621) Balance at December 31, 2018 $ 13,779

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2018
Marketable Securities
Summary of marketable securities, classified as available-for-sale	Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value (In thousands) December 31, 2018 Marketable securities U.S. government and municipal obligations Maturing in one year or less $ 27,355 $ — $ (4) $ 27,351 Maturing after one year through three years — — — — Total U.S. government and municipal obligations $ 27,355 $ — $ (4) $ 27,351 Corporate debt securities Maturing in one year or less $ 42,370 $ — $ (9) $ 42,361 Maturing after one year through three years — — — — Total corporate debt securities $ 42,370 $ — $ (9) $ 42,361 Total marketable securities $ 69,725 $ — $ (13) $ 69,712 December 31, 2017 Marketable securities U.S. government and municipal obligations Maturing in one year or less $ 26,164 $ 3 $ (9) $ 26,158 Maturing after one year through three years — — — — Total U.S. government and municipal obligations $ 26,164 $ 3 $ (9) $ 26,158 Corporate debt securities Maturing in one year or less $ 73,007 $ 1 $ (27) $ 72,981 Maturing after one year through three years — — — — Total corporate debt securities $ 73,007 $ 1 $ (27) $ 72,981 Total marketable securities $ 99,171 $ 4 $ (36) $ 99,139

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Property and Equipment, Net
Schedule of property and equipment	December 31, December 31, 2018 2017 (In thousands) Laboratory Equipment $ 8,272 $ 7,770 Manufacturing Equipment 2,497 4,354 Office Furniture and Equipment 3,791 3,764 Leasehold Improvements 17,408 17,164 Construction in Progress 327 932 Total Property and Equipment 32,295 33,984 Less: Accumulated Depreciation and Amortization (26,184) (23,612) Property and Equipment, Net $ 6,111 $ 10,372

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2018
Accrued Expenses
Schedule of accrued expenses	December 31, December 31, 2018 2017 (In thousands) Accrued Payroll and Employee Benefits $ 4,400 $ 6,348 Accrued Research and Development Contract Costs 1,766 11,399 Accrued Professional Fees 620 1,408 Other Accrued Expenses 221 300 $ 7,007 $ 19,455

Other Long-Term Liabilities (Ta

Other Long-Term Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Other Long-Term Liabilities
Schedule of other long-term liabilities	December 31, December 31, 2018 2017 (In thousands) Net Deferred Tax Liabilities Related to IPR&D (Note 14) $ 3,007 $ 3,772 Deferred Income From Sale of Tax Benefits 4,218 6,756 Other 1,083 1,344 Contingent Milestones (Note 4) 13,779 43,400 Deferred Revenue 1,586 2,813 Total 23,673 58,085 Less Current Portion (4,526) (6,566) Long-Term Portion $ 19,147 $ 51,519

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2017 723,747 $ 141.00 6.1 Granted 338,517 $ 9.11 Exercised (6,967) $ 42.00 Canceled (189,165) $ 125.38 Options Outstanding at December 31, 2018 866,132 $ 93.70 7.1 Options Vested and Expected to Vest at December 31, 2018 846,352 $ 95.47 7.0 Options Exercisable at December 31, 2018 426,612 $ 162.83 5.1 Shares Available for Grant Under the 2008 Plan 356,913
Summary of restricted stock activity	Weighted Average Grant Date Fair Value Shares (per share) Outstanding and unvested at December 31, 2017 6,445 $ 44.70 Granted — $ — Vested (2,449) $ 47.94 Canceled (444) $ 34.83 Outstanding and unvested at December 31, 2018 3,552 $ 43.84
Schedule of stock-based compensation expense	2018 2017 2016 (In thousands) Research and development $ 3,874 $ 6,693 $ 7,821 General and administrative 4,207 5,619 7,496 Total stock-based compensation expense $ 8,081 $ 12,312 $ 15,317
Schedule of assumptions used for the fair value of employee stock options granted	2018 2017 2016 Expected stock price volatility 73 - 85% 75 - 77% 70 - 77% Expected option term 6.0 Years 6.0 Years 6.0 Years Risk-free interest rate 2.8 - 3.1% 2.0 - 2.3% 1.4 - 2.3% Expected dividend yield None None None

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Taxes
Schedule of components of income tax benefit (provision)	Year Ended December 31, 2018 2017 2016 (In thousands) Income Tax Benefit (Provision): Federal $ 22,255 $ 57,547 $ 45,518 State 6,406 (2,479) 7,268 Foreign 913 2,448 1,124 Income Tax Rate Change — (99,528) — 29,574 (42,012) 53,910 Deferred Tax Valuation Allowance (28,809) 66,294 (53,910) $ 765 $ 24,282 $ —
Schedule of reconciliation between the amount of reported income tax and the amount computed using the U.S. Statutory rate	2018 2017 2016 (In thousands) Pre-Tax Loss $ (151,949) $ (117,313) $ (128,530) Loss at Statutory Rates (31,909) (39,887) (43,700) Difference in Foreign Tax Rates — 326 150 Research and Development Credits (2,056) (2,847) (5,203) State Taxes (6,406) (6,283) (7,268) Income Tax Rate Change — 99,528 — Other (1,175) (321) 2,111 Milestone Abandonment (6,220) — — Intangible Impairment 19,105 — — Recognition of APIC NOLs — (5,729) — Impact of Pass-through Entities (913) (2,775) — Change in Valuation Allowance 28,809 (66,294) 53,910 Income Tax (Benefit) Provision $ (765) $ (24,282) $ —
Schedule of principal components of the deferred tax assets and liabilities	December 31, December 31, 2018 2017 (In thousands) Gross Deferred Tax Assets Net Operating Loss Carryforwards $ 168,239 $ 146,228 Foreign Net Operating Loss Carryforwards 4,485 3,572 Tax Credit Carryforwards 39,761 36,458 Deferred Research and Development Expenses 76,555 79,272 Stock-based Compensation 11,977 10,718 Fixed Assets 1,761 1,305 Deferred Revenue 13 686 Accrued Expenses and Other 183 316 302,974 278,555 Gross Deferred Tax Liabilities Other Acquired Intangibles 120 (1,792) IPR&D Intangibles (12,748) (15,992) Total Deferred Tax Assets and Liabilities 290,346 260,771 Valuation Allowance (293,353) (264,543) Net Deferred Tax Liability $ (3,007) $ (3,772)

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies
Schedule of obligations for base rent and CAM costs under facility and other non-cancelable operating leases	The following obligations for base rent and CAM costs under facility and other non‑cancelable operating leases as of December 31, 2018 do not include the exercise of renewal terms or early termination provisions (in thousands): 2019 $ 4,648 2020 3,140 2021 — 2022 — 2023 — Thereafter — Total minimum lease payments $ 7,788

Kolltan Acquisition (Tables)

Kolltan Acquisition (Tables)	12 Months Ended
	Dec. 31, 2018
Kolltan Acquisition
Schedule of acquisition-date fair value of the consideration transferred	The total consideration transferred consisted of the following (in thousands): Fair value of common stock issued for upfront payment $ 73,397 Fair value of contingent consideration 44,200 Kolltan transaction expenses paid in cash by the Company 3,768 Total consideration transferred $ 121,365
Summary of fair values of the assets acquired and liabilities assumed at the acquisition date	The following table summarizes the fair values of the assets acquired and liabilities assumed as of November 29, 2016 (in thousands): Cash and cash equivalents $ 8,160 Other current and long-term assets 799 Property and equipment, net 2,072 In-process research and development (IPR&D) 61,690 Goodwill 82,011 Deferred tax liabilities, net (23,393) Other assumed liabilities (9,974) Total $ 121,365
Schedule of the unaudited pro forma financial information	Unaudited Years Ended December 31, 2016 (In thousands) Revenue $ 6,786 Net loss $ (146,905)

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Selected Quarterly Financial Data (Unaudited)
Schedule of selected quarterly financial data (unaudited)	2018 Q1 2018 Q2 2018 Q3 2018 Q4 2018 (In thousands, except per share amounts) Total revenue $ 4,068 $ 2,763 $ 941 $ 1,764 Net loss (118,132) (16,407) (7,243) (9,402) Basic and diluted net loss per common share (12.61) (1.67) (0.66) (0.81) 2017 Q1 2017 Q2 2017 Q3 2017 Q4 2017 (In thousands, except per share amounts) Total revenue $ 1,534 $ 3,829 $ 3,924 $ 3,456 Net loss (34,261) (28,566) (26,363) (3,841) Basic and diluted net loss per common share (4.19) (3.42) (3.05) (0.42)

Nature of Business and Overvi_2

Nature of Business and Overview - (Details) $ in Thousands	Feb. 08, 2019	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)product	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Nature of Business and Overview
Number of drug candidates in clinical development | product										4
Cash, cash equivalents and marketable securities		$ 94,000								$ 94,000
Net Loss		$ (9,402)	$ (7,243)	$ (16,407)	$ (118,132)	$ (3,841)	$ (26,363)	$ (28,566)	$ (34,261)	(151,184)	$ (93,031)	$ (128,530)
Net cash used in operations										$ 75,235	$ 99,931	$ 113,036
Reverse stock split	0.067

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Basis of Presentation (Details)	12 Months Ended
	Dec. 31, 2018segment
Summary of Significant Accounting Policies
Operating segments (in segments)	1

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Concentration of Credit Risk and Significant Customers and Suppliers (Details) - Revenue - Customer concentration	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Combined BMS, Rockefeller and International AIDS Vaccine Initiative
Concentration risk
Concentration risk (as a percent)	86.00%	77.00%
Combined Rockefeller and BMS
Concentration risk
Concentration risk (as a percent)			71.00%

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2018
Laboratory equipment
Property and Equipment
Useful lives (in years)	5 years
Office furniture and equipment
Property and Equipment
Useful lives (in years)	5 years
Computer equipment
Property and Equipment
Useful lives (in years)	3 years
Manufacturing equipment | Minimum
Property and Equipment
Useful lives (in years)	7 years
Manufacturing equipment | Maximum
Property and Equipment
Useful lives (in years)	10 years

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Other Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies
Non-controlling investment	$ 1.8	$ 1.8

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Intangible assets
Non-cash impairment charge, indefinite-lived		$ 13
IPR&D
Intangible assets
Non-cash impairment charge, indefinite-lived	$ 11.8
License Rights
Intangible assets
Non-cash impairment charge, finite lived	$ 6.9

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018
Goodwill
Goodwill asset impaired		$ 90,976
Glemba
Goodwill
Goodwill asset impaired	$ 91,000

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Foreign Currency Translation (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies
Unrealized gain related to foreign currency translation included in AOCI	$ 2.6	$ 2.6

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net loss per share
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	869,684	730,192	684,581
Stock options
Net loss per share
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	866,132	723,747	681,248
Restricted Stock
Net loss per share
Potentially dilutive common shares not been included in net loss per common share calculations because the effect would have been anti-dilutive	3,552	6,445	3,333

Summary of Significant Accou_12

Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - ASU 2016-02 - Forecast $ in Millions	Jan. 01, 2019USD ($)
Newly-Adopted Accounting Pronouncements
Right of use asset	$ 4.2
Lease liability	$ 4.7

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income
Period Start Balance	$ 236,369	$ 265,431	$ 290,105
Period End Balance	124,060	236,369	265,431
Amounts reclassified from AOCI	0	0	0
Unrealized Gain/(Loss) on Marketable Securities
Accumulated Other Comprehensive Income
Period Start Balance	(32)
Other comprehensive gain	19
Period End Balance	(13)	(32)
Foreign Currency Items
Accumulated Other Comprehensive Income
Period Start Balance	2,596
Period End Balance	2,596	2,596
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income
Period Start Balance	2,564	2,541	2,307
Other comprehensive gain	19
Period End Balance	$ 2,583	$ 2,564	$ 2,541

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair value | Level 3
Liabilities:
Kolltan acquisition contingent consideration	$ 13,779	$ 43,400
Fair Value Measurements | Level 2
Assets:
Money market funds and cash equivalents	15,755	24,061
Marketable securities	69,712	99,139
Total financial assets at fair value	85,467	123,200
Fair Value Measurements | Level 3
Liabilities:
Kolltan acquisition contingent consideration	13,779	43,400
Total financial liabilities at fair value	13,779	43,400
Fair Value Measurements | Fair value
Assets:
Money market funds and cash equivalents	15,755	24,061
Marketable securities	69,712	99,139
Total financial assets at fair value	85,467	123,200
Liabilities:
Kolltan acquisition contingent consideration	13,779	43,400
Total financial liabilities at fair value	$ 13,779	$ 43,400

Fair Value Measurements - Conti

Fair Value Measurements - Contingent Consideration Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Roll-forward of acquisition-related contingent consideration
Fair value adjustments included in operating expenses	$ (29,621)	$ (800)
Fair value | Level 3
Roll-forward of acquisition-related contingent consideration
Balance at beginning of period	43,400
Fair value adjustments included in operating expenses	(29,621)
Balance at end of period	$ 13,779	$ 43,400

Fair Value Measurements - Addit

Fair Value Measurements - Additional information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair value measurements
Gain (loss) on fair value remeasurement of contingent consideration	$ 29,621	$ 800
Kolltan | Specified development, regulatory approvals or sales-based milestones
Fair value measurements
Milestone payments	127,500
Fair value
Fair value measurements
Assets level 1 to level 2 transfers	0	0
Assets level 2 to level 1 transfers	0	0
Liabilities level 1 to level 2 transfers	0	0
Liabilities level 2 to level 1 transfers	0	0
Asset transfer out of level 3	0	0
Asset transfer into level 3	0	0
Liabilities transfers out of level 3	0	0
Liabilities transfers into level 3	$ 0	$ 0

Marketable Securities (Details)

Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Amortized Cost
Amortized cost	$ 69,725	$ 99,171
Gross Unrealized Gains
Gross Unrealized Gains		4
Gross Unrealized Losses
Gross Unrealized Losses	(13)	(36)
Fair Value
Fair Value	69,712	99,139
U.S. government and municipal obligations
Amortized Cost
Maturing in one year or less	27,355	26,164
Amortized cost	27,355	26,164
Gross Unrealized Gains
Maturing in one year or less		3
Gross Unrealized Gains		3
Gross Unrealized Losses
Maturing in one year or less	(4)	(9)
Gross Unrealized Losses	(4)	(9)
Fair Value
Maturing in one year or less	27,351	26,158
Fair Value	27,351	26,158
Corporate debt securities
Amortized Cost
Maturing in one year or less	42,370	73,007
Amortized cost	42,370	73,007
Gross Unrealized Gains
Maturing in one year or less		1
Gross Unrealized Gains		1
Gross Unrealized Losses
Maturing in one year or less	(9)	(27)
Gross Unrealized Losses	(9)	(27)
Fair Value
Maturing in one year or less	42,361	72,981
Fair Value	$ 42,361	$ 72,981

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Number of investment-grade securities in unrealized loss position over 12 months	$ 0
Interest Receivable	$ 100	$ 300

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment
Total Property and Equipment	$ 32,295	$ 33,984
Less Accumulated Depreciation and Amortization	(26,184)	(23,612)
Property and Equipment, Net	6,111	10,372
Depreciation and amortization expense	3,577	4,414	$ 3,095
Laboratory equipment
Property and Equipment
Total Property and Equipment	8,272	7,770
Manufacturing equipment
Property and Equipment
Total Property and Equipment	2,497	4,354
Office furniture and equipment
Property and Equipment
Total Property and Equipment	3,791	3,764
Leasehold Improvements
Property and Equipment
Total Property and Equipment	17,408	17,164
Construction in Progress
Property and Equipment
Total Property and Equipment	$ 327	$ 932

Intangible Assets and Goodwill

Intangible Assets and Goodwill - Intangible Assets, Net (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Intangible assets
Finite-lived intangible assets		$ 0	$ 7,100
Non-cash impairment charge, indefinite-lived			13,000
Indefinite-lived intangible assets		48,700	60,500
Amortization of Acquired Intangible Assets		$ 224	$ 896	$ 997
IPR&D
Intangible assets
Non-cash impairment charge, indefinite-lived	$ 11,800
License Rights
Intangible assets
Non-cash impairment charge, finite lived	$ 6,900

Intangible Assets and Goodwil_2

Intangible Assets and Goodwill - Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Goodwill
Goodwill			$ 90,976
Goodwill asset impaired		$ 90,976
Glemba
Goodwill
Amount of carrying amount in excess of fair value amount		$ 91,000
Goodwill asset impaired	$ 91,000

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Expenses
Accrued Payroll and Employee Benefits	$ 4,400	$ 6,348
Accrued Research and Development Contract Costs	1,766	11,399
Accrued Professional Fees	620	1,408
Other Accrued Expenses	221	300
Accrued Expenses	$ 7,007	$ 19,455

Other Long-Term Liabilities (De

Other Long-Term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other Long-Term Liabilities
Net Deferred Tax Liabilities Related to IPR&P (Note 14)	$ 3,007	$ 3,772
Deferred Income From Sale of Tax Benefits	4,218	6,756
Other	1,083	1,344
Contingent Milestones (Note 4)	13,779	43,400
Deferred Revenue	1,586	2,813
Total	23,673	58,085
Less Current Portion	(4,526)	(6,566)
Long-Term Portion	$ 19,147	$ 51,519

Other Long-Term Liabilities- Ne

Other Long-Term Liabilities- New Jersey tax benefits (Details) - USD ($) $ in Thousands	1 Months Ended			12 Months Ended
	Nov. 30, 2015	Dec. 31, 2014	Jan. 31, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment and other income				$ 4,487	$ 4,214	$ 4,386
New Jersey tax benefits
Amount of tax benefit	$ 9,800	$ 1,900	$ 1,100
Proceeds from sale of tax credits	$ 9,200	$ 1,800	$ 1,000
Base of operations requirement (in years)				5 years
Investment and other income				$ 2,500	$ 2,700	$ 2,800

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock (Details) - USD ($) $ in Thousands	1 Months Ended		2 Months Ended	12 Months Ended
	Nov. 30, 2017	May 31, 2016	Feb. 28, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 13, 2017
Common Stock
Maximum aggregate offering price of securities available for sale							$ 250,000
Aggregate offering price stock sale		$ 60,000
Additional offering price stock sale authorized	$ 75,000
Net proceeds from sale of common stock				$ 29,022	$ 51,025	$ 13,946
Common Stock
Common Stock
Shares Issued in Connection with Cantor Agreement (in shares)				2,702,660	1,181,524	220,253
Aggregate gross offering price available				$ 37,600
Common Stock | Subsequent Event
Common Stock
Common stock issued (in shares)			478,785
Net proceeds from sale of common stock			$ 2,300

Stockholders' Equity - Converti

Stockholders' Equity - Convertible Preferred Stock (Details) - shares	Dec. 31, 2018	Dec. 31, 2017
Preferred stock, shares authorized	3,000,000	3,000,000
Preferred stock, shares outstanding	0	0
Series C-1 Preferred Stock
Preferred stock, shares authorized	350,000
Preferred stock, shares outstanding	0	0

Stock-Based Compensation - Empl

Stock-Based Compensation - Employee Stock Purchase Plan (Details) - Employee Stock Purchase Plan - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-Based Compensation
Common stock reserved for issuance (in shares)	26,667
Purchase price of fair value of common stock (in percent)	85.00%
Issued (in shares)	9,524	5,359	3,956
Available for issuance (in shares)	3,666

Stock-Based Compensation - Em_2

Stock-Based Compensation - Employee Stock Option and Incentive Plan (Details) - Stock options	12 Months Ended
	Dec. 31, 2018shares
Stock-Based Compensation
Common stock authorized grants (in shares)	1,333,333
Vesting period (in years)	4 years
Expiration period (in years)	10 years
Principal Owner
Stock-Based Compensation
Expiration period (in years)	5 years
Exercise price as a percentage of fair market value	110.00%

Stock-Based Compensation - Em_3

Stock-Based Compensation - Employee Stock Option and Incentive Plan Activity (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Shares
Options Outstanding at beginning of the period (in shares)	723,747
Granted (in shares)	338,517
Exercised (in shares)	(6,967)
Canceled (in shares)	(189,165)
Options Outstanding at the end of the period (in shares)	866,132	723,747
Options Vested and Expected to Vest at the end of the period (in shares)	846,352
Options Exercisable at the end of the period (in shares)	426,612
Shares Available for Grant Under the 2008 Plan	356,913
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 141
Granted (in dollars per share)	9.11
Exercised (in dollars per share)	42
Canceled (in dollars per share)	125.38
Options Outstanding at the end of the period (in dollars per share)	93.70	$ 141
Options Vested and Expected to Vest at the end of the period (in dollars per share)	95.47
Options Exercisable at the end of the period (in dollars per share)	$ 162.83
Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at the end of the period	7 years 1 month 6 days	6 years 1 month 6 days
Options Vested and Expected to Vest at the end of the period	7 years
Options Exercisable at the end of the period	5 years 1 month 6 days

Stock-Based Compensation - Em_4

Stock-Based Compensation - Employee Stock Option and Incentive Plan Activity Additional Information (Details) - Stock options - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Additional information
Intrinsic value of options exercised	$ 0	$ 0	$ 0.1
Weighted average grant-date fair value (in dollars per share)	$ 6.60	$ 23.70	$ 47.70
Fair value of options vested	$ 8	$ 13.4	$ 17
Intrinsic value of options outstanding	0
Intrinsic value of options vested and expected to vest	0
Compensation cost not yet recognized	$ 6.8
Weighted average period compensation cost is expected to be recognized (in years)	2 years 7 months 6 days

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock (Details) - Restricted Stock	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Shares
Outstanding and unvested at the beginning of the period (in shares) | shares	6,445
Vested (in shares) | shares	(2,449)
Canceled (in shares) | shares	(444)
Outstanding and unvested at the end of the period (in shares) | shares	3,552
Weighted Average Grant Date Fair Value (per share)
Outstanding and unvested at the beginning of the period (in dollars per share) | $ / shares	$ 44.70
Vested (in dollars per share) | $ / shares	47.94
Canceled (in dollars per share) | $ / shares	34.83
Outstanding and unvested at the end of the period (in dollars per share) | $ / shares	$ 43.84

Stock-Based Compensation - Expe

Stock-Based Compensation - Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation expense
Stock-based compensation expense	$ 8,081	$ 12,312	$ 15,317
Research and development
Stock-based compensation expense
Stock-based compensation expense	3,874	6,693	7,821
General and administrative
Stock-based compensation expense
Stock-based compensation expense	$ 4,207	$ 5,619	$ 7,496

Stock-Based Compensation - Valu

Stock-Based Compensation - Valuation (Details) - Stock options	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Black-Scholes option with following assumptions:
Expected stock price volatility, minimum (as a percent)	73.00%	75.00%	70.00%
Expected stock price volatility, maximum (as a percent)	85.00%	77.00%	77.00%
Expected option term	6 years	6 years	6 years
Risk-free interest rate, minimum (as a percent)	2.80%	2.00%	1.40%
Risk-free interest rate, maximum (as a percent)	3.10%	2.30%	2.30%

Revenue (Details)

Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014	Jan. 01, 2018
Revenue
Accumulated Deficit	$ (962,438)	$ (812,517)
Deferred Revenue	1,586	2,813
Accounts receivable	3,162	1,880
Revenue recognized from contract liabilities	1,900
Revenues	9,538	12,743	$ 6,786
ASU 2014-09
Revenue
Accumulated Deficit					$ (1,300)
Deferred Revenue					(800)
Accounts receivable					$ 500
Product Development and Licensing Agreements
Revenue
Revenues	3,341	3,153	2,174
Contracts and Grants
Revenue
Revenues	6,197	9,590	4,612
Bristol-Myers Squibb Company | Product Development and Licensing Agreements
Revenue
Deferred Revenue				$ 5,000
Reimbursement of external costs (as percent)				50.00%
Revenues	3,300	2,800	2,100
IAVI & Frontier | Contracts and Grants
Revenue
Revenues	3,000	6,600
Rockefeller | Contracts and Grants
Revenue
Revenues	$ 2,600	$ 2,200	$ 2,700

Collaboration Agreements (Detai

Collaboration Agreements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaborative Agreements
License fee expense	$ 0.7	$ 0.7	$ 1.6
Type of cost of goods sold line item	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Southampton
Collaborative Agreements
Potential milestone payment	$ 1
Amgen
Collaborative Agreements
Potential milestone payment	0.9
Yale
Collaborative Agreements
Potential milestone payment	3
MedImmune | Obtaining specified regulatory and development
Collaborative Agreements
Potential milestone payment	45
MedImmune | Specified annual net sales thresholds are met
Collaborative Agreements
Potential milestone payment	$ 125

Income Taxes - Benefit (Provisi

Income Taxes - Benefit (Provision) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Benefit (Provision):
Federal	$ 22,255	$ 57,547	$ 45,518
State	6,406	(2,479)	7,268
Foreign	913	2,448	1,124
Income Tax Rate Change		(99,528)
Income tax benefit (provision) before valuation allowance	29,574	(42,012)	53,910
Deferred tax valuation allowance	(28,809)	66,294	$ (53,910)
Income Tax Benefit (Provision)	$ 765	$ 24,282

Income Taxes - Reconciliation (

Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation between the amount of reported income tax and the amount computed using U.S. Statutory rate
Pre-tax loss	$ (151,949)	$ (117,313)	$ (128,530)
Loss at Statutory Rates	(31,909)	(39,887)	(43,700)
Difference in Foreign Tax Rates		326	150
Research and Development Credits	(2,056)	(2,847)	(5,203)
State Taxes	(6,406)	(6,283)	(7,268)
Income Tax Rate Change		99,528
Other	(1,175)	(321)	2,111
Milestone Abandonment	(6,220)
Intangible Impairment	19,105
Recognition of APIC NOLs		(5,729)
Impact of Pass-through Entities	(913)	(2,775)
Change in Valuation Allowance	28,809	(66,294)	$ 53,910
Income Tax (Benefit) Provision	$ (765)	$ (24,282)

Income Taxes - Deferred Tax (De

Income Taxes - Deferred Tax (Details) - USD ($) $ in Thousands	Dec. 22, 2017	Dec. 31, 2018	Dec. 31, 2017
Gross Deferred Tax Assets
Net Operating Loss Carryforwards		$ 168,239	$ 146,228
Foreign Net Operating Loss Carryforwards		4,485	3,572
Tax Credit Carryforwards		39,761	36,458
Deferred Research and Development Expenses		76,555	79,272
Stock-based Compensation		11,977	10,718
Fixed Assets		1,761	1,305
Deferred Revenue		13	686
Accrued Expenses and Other		183	316
Deferred Tax Assets, Gross		302,974	278,555
Gross Deferred Tax Liabilities
Other Acquired Intangibles		120	(1,792)
IPR&D Intangibles		(12,748)	(15,992)
Total Deferred Tax Assets and Liabilities		290,346	260,771
Valuation Allowance		(293,353)	(264,543)
Net Deferred Tax Liability		(3,007)	(3,772)
Principal components of the deferred tax assets and liabilities
Increase in deferred tax and valuation allowance			$ 17,700
U.S. federal corporate income tax rate (as a percent)	21.00%		35.00%
U.S. federal corporate income tax net operating losses (as a percent)	80.00%
Change in tax rate, deferred tax liability benefit		6,900
Additional income tax benefit leading to tax liabilities		12,200
Revaluation of deferred tax asset		99,500
Income tax expense (benefit)		$ (765)	$ (24,282)

Income Taxes - Carryforwards (D

Income Taxes - Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards
Foreign pre-tax loss	$ 3	$ 8.2
Federal
Operating Loss Carryforwards
Net operating loss carryforwards	636.8
Net operating loss carryforwards with no expiration date	75
Federal | R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	31
State
Operating Loss Carryforwards
Net operating loss carryforwards	532.4
State | R&D credit
Operating Loss Carryforwards
Tax credit carryforwards	$ 11.1

Commitments and Contingencies_2

Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Obligations for base rent and CAM costs under facility and other non-cancelable operating leases
2,019	$ 4,648
2,020	3,140
Total minimum lease payments	7,788
Total rent and CAM expense	$ 4,000	$ 4,100	$ 4,800

Retirement Savings Plan (Detail

Retirement Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Savings Plan
Maximum contribution by participants (as a percent)	60.00%
Employer matching contributions (as a percent)	50.00%
Maximum percentage of employees' gross pay subject to employer matching contributions	4.00%
Benefit expense for the 401(k) Plan	$ 0.4	$ 0.5	$ 0.4

Kolltan Acquisition (Details)

Kolltan Acquisition (Details) - Kolltan - USD ($) $ in Millions	Nov. 29, 2016	Dec. 31, 2018
Kolltan Acquisition
Shares issued as part of consideration (in shares)	1,217,200
Specified development, regulatory approvals or sales-based milestones
Kolltan Acquisition
Milestone payments		$ 127.5

Kolltan Acquisition - Purchase

Kolltan Acquisition - Purchase Price (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 29, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Acquisition-date fair value of consideration transferred
Fair value of contingent consideration				$ 13,779	$ 43,400
Kolltan transaction expenses paid in cash by the Company		$ 700	$ 700
Kolltan
Kolltan Acquisition
Price of common stock (in dollars per share)	$ 60.30
Acquisition-date fair value of consideration transferred
Fair value of common stock issued for upfront payment	$ 73,397
Fair value of contingent consideration	44,200
Kolltan transaction expenses paid in cash by the Company	3,768
Total consideration transferred	$ 121,365

Kolltan Acquisition - Allocatio

Kolltan Acquisition - Allocations of Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Nov. 29, 2016
Kolltan Acquisition
Estimated development costs included in expected future net cash flows	$ 132,000
Goodwill expected to be deductible for income tax purposes			$ 0
Summary of fair values of assets acquired and liabilities assumed
Goodwill		$ 90,976
Kolltan
Summary of fair values of assets acquired and liabilities assumed
Cash and cash equivalents			8,160
Other current and long-term assets			799
Property and equipment, net			2,072
In-process research and development (IPR&D)			61,690
Goodwill			82,011
Deferred tax liabilities, net			(23,393)
Other assumed liabilities			(9,974)
Total			121,365
Kolltan | Anti-KIT Program
Summary of fair values of assets acquired and liabilities assumed
In-process research and development (IPR&D)			40,000
Kolltan | CDX-3379
Summary of fair values of assets acquired and liabilities assumed
In-process research and development (IPR&D)			3,500
Kolltan | TAM programs
Summary of fair values of assets acquired and liabilities assumed
In-process research and development (IPR&D)			$ 18,000

Kolltan Acquisition - Acquisiti

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

Kolltan Acquisition - Pro Forma

Kolltan Acquisition - Pro Forma (Details) - USD ($) $ in Thousands	Nov. 29, 2016	Dec. 31, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Kolltan Acquisition
Transaction expense		$ 700									$ 700
Revenue			$ 1,764	$ 941	$ 2,763	$ 4,068	$ 3,456	$ 3,924	$ 3,829	$ 1,534
Kolltan
Kolltan Acquisition
Severance expense		3,100
Transaction expense	$ 3,768
Revenue		$ 0
Pro Forma Financial Information
Revenue											6,786
Net loss											$ (146,905)

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Data (Unaudited)
Total revenue	$ 1,764	$ 941	$ 2,763	$ 4,068	$ 3,456	$ 3,924	$ 3,829	$ 1,534
Net loss	$ (9,402)	$ (7,243)	$ (16,407)	$ (118,132)	$ (3,841)	$ (26,363)	$ (28,566)	$ (34,261)	$ (151,184)	$ (93,031)	$ (128,530)
Basic and diluted net loss per common share (in dollars per share)	$ (0.81)	$ (0.66)	$ (1.67)	$ (12.61)	$ (0.42)	$ (3.05)	$ (3.42)	$ (4.19)	$ (14.48)	$ (10.86)	$ (18.99)