Immunogen (IMGN) 10-K 1 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 19, 2019	Jun. 30, 2018
Document and Entity Information
Entity Registrant Name	IMMUNOGEN INC
Entity Central Index Key	855,654
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	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 1,425,536,472
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		149,409,825
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($)	Dec. 31, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	$ 262,252,000	$ 267,107,000
Accounts receivable	1,701,000	2,649,000
Unbilled revenue	617,000	2,580,000
Contract asset	500,000
Non-cash royalty receivable	9,249,000
Inventory	0	1,038,000
Prepaid and other current assets	4,462,000	2,967,000
Total current assets	278,781,000	276,341,000
Property and equipment, net of accumulated depreciation	12,891,000	14,538,000
Other assets	3,709,000	3,797,000
Total assets	295,381,000	294,676,000
LIABILITIES AND SHAREHOLDERS' EQUITY (DEFICIT)
Accounts payable	11,365,000	8,562,000
Accrued compensation	11,796,000	11,473,000
Other accrued liabilities	20,465,000	15,767,000
Current portion of deferred lease incentive	837,000	784,000
Current portion of liability related to the sale of future royalties, net of deferred financing costs of $753 and $772, respectively	25,880,000	17,779,000
Current portion of deferred revenue	317,000	1,405,000
Total current liabilities	70,660,000	55,770,000
Deferred lease incentive, net of current portion	4,675,000	5,129,000
Deferred revenue, net of current portion	80,485,000	93,752,000
Convertible 4.5% senior notes, net of deferred financing costs of $36 and $50, respectively	2,064,000	2,050,000
Liability related to the sale of future royalties, net of current portion and deferred financing costs of $1,536 and $2,373, respectively	122,345,000	151,634,000
Other long-term liabilities	4,180,000	4,236,000
Total liabilities	284,409,000	312,571,000
Commitments and contingencies (Note J)
Shareholders' deficit:
Preferred stock, $.01 par value; authorized 5,000 shares; no shares issued and outstanding
Common stock, $0.01 par value; authorized 200,000 shares; issued and outstanding 149,400 and 132,526 shares as of December 31, 2018 and December 31, 2017, respectively	1,494,000	1,325,000
Additional paid-in capital	1,192,813,000	1,009,362,000
Accumulated deficit	(1,183,335,000)	(1,028,582,000)
Total shareholders' equity (deficit)	10,972,000	(17,895,000)
Total liabilities and shareholders' equity (deficit)	$ 295,381,000	$ 294,676,000

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
CONSOLIDATED BALANCE SHEETS
Current portion of deferred financing costs for the liability related to the sale of future royalties	$ 753	$ 772
Interest rate (as a percent)	4.50%
Non-current deferred financing costs	$ 36	50
Noncurrent portion of deferred financing costs for the liability related to the sale of future royalties	$ 1,536	$ 2,373
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized shares	5,000	5,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares	200,000	200,000
Common stock, issued shares	149,400	132,526
Common stock, outstanding shares	149,400	132,526

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Revenues:
Total revenues	$ 21,506	$ 53,446	$ 115,447	$ 60,002
Operating Expenses:
Research and development	66,566	174,456	139,739	148,077
General and administrative	17,995	36,746	33,911	36,916
Restructuring charge	4,431	3,693	779
Total operating expenses	88,992	214,895	174,429	184,993
Loss from operations	(67,486)	(161,449)	(58,982)	(124,991)
Investment income, net	259	4,227	1,146	325
Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes	(8,665)	(10,631)	(13,682)	(20,130)
Interest expense on convertible senior notes	(2,249)	(95)	(3,040)	(138)
Non-cash debt conversion expense			(22,915)
Other (expense) income, net	(742)	(895)	1,461	117
Net loss	$ (78,883)	$ (168,843)	$ (96,012)	$ (144,817)
Basic and diluted net loss per common share (in dollar per share)	$ (0.91)	$ (1.21)	$ (0.98)	$ (1.67)
Basic and diluted weighted average common shares outstanding (in shares)	87,102	139,946	98,068	86,976
Total comprehensive loss	$ (78,883)	$ (168,843)	$ (96,012)	$ (144,817)
License and milestone fees
Revenues:
Total revenues	5,152	15,280	79,469	26,915
Royalty revenue
Revenues:
Total revenues				195
Non-cash royalty revenue related to the sale of future royalties
Revenues:
Total revenues	12,894	32,154	28,142	25,299
Research and development support
Revenues:
Total revenues	2,781	1,377	3,482	4,014
Clinical materials revenue
Revenues:
Total revenues	$ 679	$ 4,635	$ 4,354	$ 3,579

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' (DEFICIT) EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Jun. 30, 2015	$ 866	$ 743,108	$ (708,870)	$ 35,104
Balance (in shares) at Jun. 30, 2015	86,579
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss			(144,817)	(144,817)
Stock options exercised	$ 5	5,156		5,161
Stock options exercised (in shares)	555
Restricted stock award	$ 1	(1)
Restricted stock award (in shares)	75
Stock option and restricted stock compensation expense		21,868		21,868
Directors' deferred share unit compensation		380		380
Balance at Jun. 30, 2016	$ 872	770,511	(853,687)	(82,304)
Balance (in shares) at Jun. 30, 2016	87,209
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss			(78,883)	(78,883)
Restricted stock award - net of forfeitures	$ 1			1
Restricted stock award - net of forfeitures (in shares)	92
Stock option and restricted stock compensation expense		8,121		8,121
Directors' deferred share unit compensation		215		215
Balance at Dec. 31, 2016	$ 873	778,847	(932,570)	(152,850)
Balance (in shares) at Dec. 31, 2016	87,301
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss			(96,012)	(96,012)
Stock options exercised	$ 1	649		650
Stock options exercised (in shares)	191
Restricted stock award - net of forfeitures	$ 21	(21)
Restricted stock award - net of forfeitures (in shares)	2,146
Conversion of debt	$ 262	117,067		117,329
Conversion of debt (in shares)	26,160
Issuance of common stock	$ 167	101,496		101,663
Issuance of common stock (in shares)	16,675
Stock option and restricted stock compensation expense		11,119		11,119
Directors' deferred share units converted	$ 1	(1)
Directors' deferred share units converted (in shares)	53
Directors' deferred share unit compensation		206		206
Balance at Dec. 31, 2017	$ 1,325	1,009,362	(1,028,582)	$ (17,895)
Balance (in shares) at Dec. 31, 2017	132,526			132,526
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss			(168,843)	$ (168,843)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 9	4,292		4,301
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	946
Issuance of common stock	$ 158	162,354		162,512
Issuance of common stock (in shares)	15,755
Stock option and restricted stock compensation expense		16,445		16,445
Directors' deferred share units converted	$ 2	(1)		1
Directors' deferred share units converted (in shares)	173
Directors' deferred share unit compensation		361		361
Balance at Dec. 31, 2018	$ 1,494	$ 1,192,813	(1,183,335)	$ 10,972
Balance (in shares) at Dec. 31, 2018	149,400			149,400
Increase (Decrease) in Shareholders' (Deficit) Equity
Transition adjustment for ASC 606			$ 14,090	$ 14,090

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net loss	$ (78,883)	$ (168,843)	$ (96,012)	$ (144,817)
Adjustments to reconcile net loss to net cash used for operating activities:
Non-cash royalty revenue related to sale of future royalties	(12,894)	(32,154)	(28,142)	(25,299)
Non-cash interest expense on liability related to sale of future royalties and convertible senior notes	8,665	10,631	13,682	20,130
Non-cash debt conversion expense			22,915
Depreciation and amortization	3,074	7,411	5,963	5,327
Loss (gain) on sale/disposal of fixed assets and impairment charges	1,130	115	239	(21)
Stock and deferred share unit compensation	8,337	16,807	11,325	22,248
Deferred rent	88	(95)	91	161
Change in operating assets and liabilities:
Accounts receivable	(1,143)	948	(623)	4,205
Unbilled revenue	(5,369)	1,963	4,198	(695)
Inventory	(1,285)	1,038	1,154	2,028
Contract asset		(500)
Prepaid and other current assets	(505)	(1,495)	2,419	(706)
Other assets	405	88	(777)	(2,456)
Accounts payable	(3,247)	2,667	771	2,649
Accrued compensation	(3,778)	323	4,527	2,378
Other accrued liabilities	960	3,839	4,375	(1,434)
Deferred revenue	747	(9,165)	61,540	(8,318)
Proceeds from landlord for tenant improvements	42			144
Net cash (used) provided by operating activities	(83,656)	(166,422)	7,645	(124,476)
Cash flows from investing activities:
Purchases of property and equipment	(1,406)	(5,246)	(1,116)	(10,376)
Net cash used for investing activities	(1,406)	(5,246)	(1,116)	(10,376)
Cash flows from financing activities:
Proceeds from issuance of common stock under stock plans		4,301	650	5,161
Proceeds from common stock issuance, net of $395 and $222 of transaction costs, respectively		162,512	101,663
Fees for debt conversion			(1,699)
Proceeds from issuance of convertible 4.5% notes, net of $3,392 of transaction costs				96,608
Net cash provided by financing activities		166,813	100,614	101,769
Net change in cash and cash equivalents	(85,062)	(4,855)	107,143	(33,083)
Cash and cash equivalents, beginning of period	245,026	267,107	159,964	278,109
Cash and cash equivalents, end of period	$ 159,964	262,252	267,107	$ 245,026
Supplemental disclosure:
Cash paid during the year for interest		$ 95	$ 4,685

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
CONSOLIDATED STATEMENTS OF CASH FLOWS
Transaction costs	$ 395	$ 222
Interest rate (as a percent)	4.50%

Nature of Business and Plan of

Nature of Business and Plan of Operations	12 Months Ended
	Dec. 31, 2018
Nature of Business and Plan of Operations
Nature of Business and Plan of Operations	A. Nature of Business and Plan of Operations ImmunoGen, Inc. (the Company) was incorporated in Massachusetts in 1981 and is focused on the development of antibody‑drug conjugates, or ADCs. The Company has generally incurred operating losses and negative cash flows from operations since inception, incurred a net loss of approximately $168.8 million during the year ended December 31, 2018, and has an accumulated deficit of approximately $1.2 billion as of December 31, 2018. The Company has primarily funded these losses through payments received from its collaborations and equity and convertible debt financings. To date, the Company has no product revenue and management expects operating losses to continue for the foreseeable future. At December 31, 2018, the Company had $262.3 million of cash and cash equivalents on hand. The Company anticipates that its current capital resources and the $65.2 million raised from the sale of its residual rights to Kadcyla royalties in January 2019 (see Note F) will enable it to meet its operational expenses and capital expenditures for more than twelve months after these financial statements are issued. The Company may raise additional funds through equity or debt financings or generate revenues from collaborators through a combination of upfront license payments, milestone payments, royalty payments, and research funding. There can be no assurance that the Company will be able to obtain additional debt or equity financing or generate revenues from collaborators on terms acceptable to the Company or at all. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations and financial condition and require the Company to defer or limit some or all of its research, development and/or clinical projects. The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, the development by its competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, manufacturing and marketing limitations, complexities associated with managing collaboration arrangements, third‑party reimbursements, and compliance with governmental regulations. In June 2016, the Company’s Board of Directors approved a change in the Company’s fiscal year from a fiscal year ending on the last day of June of each year to a calendar fiscal year ending on the last day of December of each year, effective January 1, 2017. Accordingly, in addition to financial statements as of and for the years ended December 31, 2018 and 2017, these financial statements contain six-month transitional financial statements as of and for the period ending December 31, 2016.

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	B. Summary of Significant Accounting Policies Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, ImmunoGen Securities Corp., ImmunoGen Europe Limited, ImmunoGen (Bermuda) Ltd., ImmunoGen BioPharma (Ireland) Limited, and Hurricane, LLC. All intercompany transactions and balances have been eliminated. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States (U.S.) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Subsequent Events The Company has evaluated all events or transactions that occurred after December 31, 2018 up through the date the Company issued these financial statements. In January 2019, the Company sold its residual rights to receive royalty payments on commercial sales of Kadcyla to OMERS, the defined benefit pension plan for municipal employees in the Province of Ontario, Canada, for $65.2 million, net of fees. On March 1, 2019, the Company announced that FORWARD I did not meet its PFS primary endpoint in either the entire study population or in the pre-specified subset of patients with high-FRα expression. The Company plans to conduct a full review of the FORWARD I data to determine potential next steps with mirvetuximab as a single agent, and assess its ongoing FORWARD II combination studies as a separate path forward to support a registration in ovarian cancer. The Company did not have any other material recognizable or unrecognizable subsequent events. Adoption of ASC Topic 606, Revenue from Contracts with Customers The Company adopted Accounting Standards Codification Topic or ASC, 606 – Revenue from Contracts with Customers , (ASC 606) on January 1, 2018, using the modified retrospective method for all contracts not completed as of the date of adoption. The reported results for 2018 reflect the application of ASC 606 guidance, while the reported results prior to 2018 were prepared under the guidance of ASC 605, Revenue Recognition (ASC 605), which is also referred to herein as "legacy GAAP" or the "previous guidance." Financial Statement Impact of Adopting ASC 606 The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of December 31, 2017, was recorded as an adjustment to accumulated deficit as of the adoption date. As a result of applying the modified retrospective method to adopt the new revenue guidance, the following adjustments were made to accounts on the condensed consolidated balance sheet as of January 1, 2018: IMMUNOGEN, INC. ADJUSTED CONSOLIDATED BALANCE SHEET In thousands, except per share amounts Adjustments Balance at December 31, Due to January 1, 2017 ASC 606 2018 ASSETS Cash and cash equivalents $ 267,107 $ — $ 267,107 Accounts receivable 2,649 — 2,649 Unbilled revenue 2,580 — 2,580 Non-cash royalty receivable — 8,900 8,900 Inventory 1,038 — 1,038 Prepaid and other current assets 2,967 — 2,967 Total current assets 276,341 8,900 285,241 Property and equipment, net of accumulated depreciation 14,538 — 14,538 Other assets 3,797 — 3,797 Total assets $ 294,676 $ 8,900 $ 303,576 LIABILITIES AND SHAREHOLDERS’ DEFICIT Accounts payable $ 8,562 $ — $ 8,562 Accrued compensation 11,473 — 11,473 Other accrued liabilities 15,767 — 15,767 Current portion of deferred lease incentive 784 — 784 Current portion of liability related to the sale of future royalties, net 17,779 — 17,779 Current portion of deferred revenue 1,405 41 1,446 Total current liabilities 55,770 41 55,811 Deferred lease incentive, net of current portion 5,129 — 5,129 Deferred revenue, net of current portion 93,752 (5,231) 88,521 Convertible 4.5% senior notes, net 2,050 — 2,050 Liability related to the sale of future royalties, net 151,634 — 151,634 Other long-term liabilities 4,236 — 4,236 Total liabilities 312,571 (5,190) 307,381 Shareholders’ deficit: Preferred stock — — — Common stock 1,325 — 1,325 Additional paid-in capital 1,009,362 — 1,009,362 Accumulated deficit (1,028,582) 14,090 (1,014,492) Total shareholders’ deficit (17,895) 14,090 (3,805) Total liabilities and shareholders’ deficit $ 294,676 $ 8,900 $ 303,576 Under the previous guidance, the Company deferred revenue pertaining to the transfer of certain exclusive commercialization and development licenses, and to account for these agreements under the legacy GAAP, the Company identified the deliverables included within the agreements and evaluated which deliverables represented separate units of accounting based on whether certain criteria were met, including whether the delivered element had stand-alone value to the collaborator. The consideration received was allocated among the separate units of accounting, and the applicable revenue recognition criteria were applied to each of the separate units. Under ASC 606, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is distinct from other performance obligations, is transferred to the customer and the customer is able to use and benefit from the license. Under the previous guidance, milestones that were considered substantive because the Company contributed significant effort to the achievement of such milestones were recognized as revenue upon achievement of the milestone. Under ASC 606, if the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service, the associated milestone value is allocated to that distinct good or service. If a milestone is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method. Under ASC 606, the Company also evaluates the milestone to determine whether the milestone is probable of being achieved and estimates the amount to be included in the transaction price. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated, otherwise, such amounts are constrained and excluded from the transaction price until the probable threshold is met. The Company determined it was probable that a future $5.0 million milestone for Takeda enrolling a patient in a Phase I trial as of the date of adoption would occur and, accordingly, recorded a reduction to accumulated deficit of $4.6 million related to this previously delivered license as approximately $400,000 was allocated to undelivered rights to future technological improvements. The $5.0 million contract asset recorded for the probable milestone was netted against contract liabilities related to the specific contract. Prior to the adoption of ASC 606, the Company recognized royalty revenue when it could reliably estimate such amounts and collectability was reasonably assured. As such, the Company generally recognized revenue for sales royalties in the quarter the amounts were reported to the Company by its licensees, or one quarter following the quarter in which sales by the Company’s licensees occurred. Under ASC 606, if the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). As a result of recognizing royalties for sales in the fourth quarter of fiscal year 2017, the Company recognized a reduction to accumulated deficit of $8.9 million. The net impact of these changes resulted in a $14.1 million reduction to accumulated deficit, a $5.2 million reduction to deferred revenue and an $8.9 million increase in non-cash royalty receivable. The adoption of ASC 606 resulted in the acceleration of revenue through December 31, 2017, which in turn reduced the related net deferred tax asset by $3.9 million. As the Company fully reserves its net deferred tax assets, the impact was offset by the valuation allowance. Impact of ASC 606 Revenue Guidance on Financial Statement Line Items The following tables compare the reported condensed consolidated balance sheet and statement of operations, as of and for the year ended December 31, 2018, to the pro-forma amounts had the previous guidance been in effect: IMMUNOGEN, INC. PRO FORMA CONSOLIDATED BALANCE SHEET In thousands, except per share amounts As of December 31, 2018 Pro forma as if the previous accounting As reported was in effect ASSETS Cash and cash equivalents $ 262,252 $ 262,252 Accounts receivable 1,701 1,701 Unbilled revenue 617 617 Contract asset 500 — Non-cash royalty receivable 9,249 — Inventory — — Prepaid and other current assets 4,462 4,462 Total current assets 278,781 269,032 Property and equipment, net of accumulated depreciation 12,891 12,891 Other assets 3,709 3,709 Total assets $ 295,381 $ 285,632 LIABILITIES AND SHAREHOLDERS’ EQUITY (DEFICIT) Accounts payable $ 11,365 $ 11,365 Accrued compensation 11,796 11,796 Other accrued liabilities 20,465 20,465 Current portion of deferred lease incentive 837 837 Current portion of liability related to the sale of future royalties, net 25,880 25,880 Current portion of deferred revenue 317 297 Total current liabilities 70,660 70,640 Deferred lease incentive, net of current portion 4,675 4,675 Deferred revenue, net of current portion 80,485 83,710 Convertible 4.5% senior notes, net 2,064 2,064 Liability related to the sale of future royalties, net 122,345 122,345 Other long-term liabilities 4,180 4,180 Total liabilities 284,409 287,614 Shareholders’ equity (deficit): Preferred stock — — Common stock 1,494 1,494 Additional paid-in capital 1,192,813 1,192,813 Accumulated deficit (1,183,335) (1,196,289) Total shareholders’ equity (deficit) 10,972 (1,982) Total liabilities and shareholders’ equity (deficit) $ 295,381 $ 285,632 As a result of adoption of ASC 606, a receivable is recorded for royalties earned during the current quarter rather than one quarter in arrears under the previous guidance. Deferred revenue increased under ASC 606 due to a greater amount of the transaction prices being allocated to the future technological improvement rights under ASC 606. IMMUNOGEN, INC. PRO FORMA CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS In thousands, except per share amounts Year ended December 31, 2018 Pro forma as if the previous accounting As reported was in effect Revenues: License and milestone fees $ 15,280 $ 16,765 Non-cash royalty revenue related to the sale of future royalties 32,154 31,805 Research and development support 1,377 1,377 Clinical materials revenue 4,635 4,635 Total revenues 53,446 54,582 Operating Expenses: Research and development 174,456 174,456 General and administrative 36,746 36,746 Restructuring charge 3,693 3,693 Total operating expenses 214,895 214,895 Loss from operations (161,449) (160,313) Investment income, net 4,227 4,227 Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes (10,631) (10,631) Interest expense on convertible senior notes (95) (95) Other (expense) income, net (895) (895) Net loss $ (168,843) $ (167,707) Basic and diluted net loss per common share $ $ Under the previous guidance, non-cash royalty revenue would have been lower than the amount recorded for the year ended December 31, 2018, due to higher Kadcyla sales in the fourth quarter of 2018 versus 2017 (because under the previous guidance, the Company recorded the royalties one quarter in arrears as previously described). License and milestone fee revenue for the year ended December 31, 2018 would have been higher due to a $5.0 million milestone that would have been included as license and milestone fee revenue in 2018 under the legacy accounting, however, due to its probability of occurring at the time of transition to ASC 606, it was recognized as part of the transition adjustment. Partially offsetting this change, less license and milestone fee revenue would have been recognized under the previous guidance related to a partner foregoing its remaining rights under a right-to-test agreement upon expiration in March 2018, as well as partners terminating their rights under certain development and commercialization licenses during the year. A greater amount of the transaction price was allocated to the expired and terminated material rights under ASC 606 than under the previous guidance. The adoption of ASC 606 had no aggregate impact on the Company’s cash flows from operations. The aforementioned impact resulted in offsetting shifts in cash flows through net losses and working capital accounts. Revenue Recognition The Company enters into licensing and development agreements with collaborators for the development of ADCs. The terms of these agreements contain multiple deliverables/performance obligations which may include (i) licenses, or options to obtain licenses, to the Company’s ADC technology, (ii) rights to future technological improvements, (iii) research activities to be performed on behalf of the collaborative partner, (iv) delivery of cytotoxic agents, and (v) prior to the decommission of the Company’s Norwood facility in 2018, the manufacture of preclinical or clinical materials for the collaborative partner. Payments to the Company under these agreements may include upfront fees, option fees, exercise fees, payments for research activities, payments for the manufacture of preclinical or clinical materials, payments based upon the achievement of certain milestones, and royalties on product sales. Prior to 2018, the Company identified the deliverables included within the agreement and evaluated which deliverables represented separate units of accounting based on whether certain criteria are met, including whether the delivered element had stand‑alone value to the collaborator in accordance with ASC 605. The consideration received was allocated among the separate units of accounting, and the applicable revenue recognition criteria were applied to each of the separate units. In 2018, revenue is recognized when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services in accordance with ASC 606. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under the agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when or as the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when or as the performance obligation is satisfied. As part of the accounting for the arrangement, the Company must develop assumptions that require judgment to determine the selling price for each deliverable under ASC 605 and performance obligation under ASC 606 that were identified in the contract, which is discussed in further detail below. At December 31, 2018, the Company had the following material types of agreements with the parties identified below: · Development and commercialization licenses, which provide the party with the right to use the Company’s ADC technology and/or certain other intellectual property to develop and commercialize anticancer compounds to a specified antigen target: Bayer (one exclusive single-target license) Biotest (one exclusive single-target license) CytomX (one exclusive single-target license) Debiopharm (one exclusive single-compound license) Fusion Pharmaceuticals (one exclusive single-target license) Novartis (five exclusive single-target licenses) Oxford BioTherapeutics/Menarini (one exclusive single target license sublicensed from Amgen) Roche, through its Genentech unit (five exclusive single-target licenses) Sanofi (five fully-paid, exclusive single-target licenses) Takeda, through its wholly owned subsidiary, Millennium Pharmaceuticals, Inc. (one exclusive single-target license) · Collaboration and option agreement for a defined period of time to secure development and commercialization licenses to develop and commercialize specified anticancer compounds on established terms: Jazz Pharmaceuticals · Collaboration and license agreement to co-develop and co-commercialize a specified anticancer compound on established terms: MacroGenics There are no performance, cancellation, termination, or refund provisions in any of the arrangements that contain material financial consequences to the Company. Development and Commercialization Licenses The obligations under a development and commercialization license agreement generally include the license to the Company’s ADC technology with respect to a specified antigen target, and may also include obligations related to rights to future technological improvements, research activities to be performed on behalf of the collaborative partner and the manufacture of preclinical or clinical materials for the collaborative partner. Generally, development and commercialization licenses contain non‑refundable terms for payments and, depending on the terms of the agreement, provide that the Company will (i) at the collaborator’s request, provide research services at negotiated prices which are generally consistent with what other third parties would charge, (ii) prior to the decommissioning of the Company’s Norwood facility in 2018, at the collaborator’s request, manufacture and provide preclinical and clinical materials or deliver cytotoxic agents at negotiated prices which are generally consistent with what other third parties would charge, (iii) earn payments upon the achievement of certain milestones, and (iv) earn royalty payments, generally until the later of the last applicable patent expiration or 10 to 12 years after product launch. Royalty rates may vary over the royalty term depending on the Company’s intellectual property rights and/or the presence of comparable competing products. In the case of Sanofi, its licenses are fully-paid and no further milestones or royalties will be received. In the case of Debiopharm, no royalties will be received. The Company may provide technical assistance and share any technology improvements with its collaborators during the term of the collaboration agreements. The Company does not directly control when or whether any collaborator will request research or, achieve milestones or become liable for royalty payments. In determining the units of accounting under ASC 605, management evaluated whether the license had stand‑alone value from the undelivered elements to the collaborative partner based on the consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research capabilities of the partner and the availability of ADC technology research expertise in the general marketplace. If the Company concluded that the license had stand‑alone value and therefore accounted for as a separate unit of accounting, the Company then determined the estimated selling prices of the license and all other units of accounting. In determining the performance obligations under ASC 606, management evaluates whether the license is distinct, and has significant standalone functionality, from the undelivered elements to the collaborative partner based on the consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research capabilities of the partner and the availability of ADC technology research expertise in the general marketplace and whether technological improvements are required for the continued functionality of the license. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. The Company determined that the estimated selling price under ASC 605 and the stand-alone selling price under ASC 606 to be consistent. The estimates the selling prices of the license and all other deliverables under ASC 605 and performance obligations under ASC 606 are based on market conditions, similar arrangements entered into by third parties, and entity‑specific factors such as the terms of the Company’s previous collaborative agreements, recent preclinical and clinical testing results of therapeutic products that use the Company’s ADC technology, the Company’s pricing practices and pricing objectives, the likelihood that technological improvements will be made, and, if made, will be used by the Company’s collaborators and the nature of the research services to be performed on behalf of its collaborators and market rates for similar services. The Company recognizes revenue related to research services under ASC 605 and ASC 606 as the services are performed. The Company performs research activities, including developing antibody specific conjugation processes, on behalf of its collaborators and potential collaborators during the early evaluation and preclinical testing stages of drug development. The Company also develops conjugation processes for materials for later stage testing and commercialization for certain collaborators. The Company is compensated at negotiated rates that are consistent with what other third parties would charge and may receive milestone payments for developing these processes which are also recorded as a component of research and development support revenue. The Company may also produce research material for potential collaborators under material transfer agreements. The Company records amounts received for research materials produced or services performed as a component of research and development support revenue. The Company may also provide cytotoxic agents to its collaborators and previously produced preclinical and clinical materials (drug substance) at negotiated prices generally consistent with what other third parties would charge. The Company recognizes revenue on cytotoxic agents and, previously, on preclinical and clinical materials when the materials have passed all quality testing required for collaborator acceptance and control has transferred under ASC 606 to the collaborator, while ASC 605 required title and risk of loss to transfer. The majority of the Company’s costs to produce these preclinical and clinical materials were fixed and then allocated to each batch based on the number of batches produced during the period. Therefore, the Company’s costs to produce these materials were significantly affected by the number of batches produced during the period. The volume of preclinical and clinical materials the Company produced was directly related to the scale and scope of preclinical activities and the number of clinical trials the Company and its collaborators were preparing for or currently had underway, the speed of enrollment in those trials, the dosage schedule of each clinical trial and the time period such trials last. Accordingly, the volume of preclinical and clinical materials produced, and therefore the Company’s per‑batch costs to manufacture these preclinical and clinical materials, varied significantly from period to period, which affected the margins recognized on such product sales. The Company recognizes revenue related to the rights to future technological improvements under ASC 605 and ASC 606 over the estimated term of the applicable license. The Company’s development and commercialization license agreements have milestone payments which for reporting purposes are aggregated into three categories: (i) development milestones, (ii) regulatory milestones, and (iii) sales milestones. Development milestones are typically payable when a product candidate initiates or advances into different clinical trial phases. Regulatory milestones are typically payable upon submission for marketing approval with the U.S. Food and Drug Administration, or FDA, or other countries’ regulatory authorities or on receipt of actual marketing approvals for the compound or for additional indications. Sales milestones are typically payable when annual sales reach certain levels. Under ASC 605, at the inception of each agreement that includes milestone payments, the Company evaluated whether each milestone was substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation included an assessment of whether (a) the consideration was commensurate with either (1) the entity’s performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the entity’s performance to achieve the milestone, (b) the consideration related solely to past performance and (c) the consideration was reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone and whether the milestone consideration was reasonable relative to all deliverables and payment terms in the arrangement in making this assessment. Non‑refundable development and regulatory milestones that were expected to be achieved as a result of the Company’s efforts during the period of substantial involvement were considered substantive and were recognized as revenue upon the achievement of the milestone, assuming all other revenue recognition criteria under ASC 605 were met. Milestones that were not considered substantive because the Company did not contribute effort to the achievement of such milestones were generally achieved after the period of substantial involvement and were recognized as revenue upon achievement of the milestone, as there were no undelivered elements remaining and no continuing performance obligations, assuming all other revenue recognition criteria under ASC 605 were met. Under ASC 606, at the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service. If the milestone payment is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method. In addition, the Company evaluates the milestone to determine whether the milestone is considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated; otherwise, such amounts are considered constrained and excluded from the transaction price. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development or regulatory milestones and any related constraint, and if necessary, adjusts its estimate of the transaction price. Any such adjustments to the transaction price are allocated to the performance obligations on the same basis as at contract inception. Amounts allocated to a satisfied performance obligation shall be recognized as revenue, or as a reduction of revenue, in the period in which the transaction price changes. For development and commercialization license agreements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue under ASC 606 at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied) in accordance with the royalty recognition constraint. Under the Company’s development and commercialization license agreements, except for the Sanofi and Debiopharm licenses, the Company receives royalty payments based upon its licensees’ net sales of covered products. Generally, under the development and commercialization agreements, the Company receives royalty reports and payments from its licensees approximately one quarter in arrears. The Company estimates the amount of royalty revenue to be recognized based on historical and forecasted sales and/or sales information from its licensees if available. Under ASC 605, royalty revenue was recognized when it could reliably estimate such amounts and collectability was reasonably assured. As such, the Company generally recognized revenue for sales royalties in the quarter the amounts were reported to the Company by its licensees, or one quarter following the quarter in which sales by the Company’s licensees occurred. Collaboration and Option Agreements/Right-to-Test Agreements The Company’s right-to-test agreements provide collaborators the right to test the Company’s ADC technology for a defined period of time through a research, or right‑to‑test, license. Under both right-to-test agreements and collaboration and option agreements, collaborators may (a) take options, for a defined period of time, to specified targets and (b) upon exercise of those options, secure or “take” licenses to develop and commercialize products for the specified targets on established terms. Under these agreements, fees may be due to the Company (i) at the inception of the arrangement (referred to as “upfront” fees or payments), (ii) upon the opt-in to acquire a development and commercialization license(s) (referred to as exercise fees or payments earned, if any, when the development and commercialization license is “taken”), (iii) at the collaborator’s request, after providing research services at negotiated prices which are generally consistent with what other third parties would charge, or (iv) some combination of all of these fees. The accounting for collaboration and option agreements and right-to-test agreements under ASC 605 and ASC 606 is dependent on the nature of the options granted to the collaborative partner. Under ASC 605, options are considered substantive if, at the inception of the agreement, the Company is at risk as to whether the collaborative partner will choose to exercise the options to secure development and commercialization licenses. Factors that are considered in evaluating whether options are substantive include the overall objective of the arrangement, the benefit the collaborator might obtain from the agreement without

Agreements

Agreements	12 Months Ended
	Dec. 31, 2018
Agreements
Agreements	C. Agreements Significant Collaborative Agreements Roche In 2000, the Company granted Genentech, now a unit of Roche, an exclusive development and commercialization license to use the Company’s maytansinoid ADC technology with antibodies, such as trastuzumab, or other proteins that target HER2. Under the terms of this agreement, Roche has exclusive worldwide rights to develop and commercialize maytansinoid ADC compounds targeting HER2. In 2013, the HER2‑targeting ADC, Kadcyla, was approved for marketing in the U.S., Japan, and the European Union, or EU. Roche has also received marketing approval in various other countries around the world. Roche is responsible for the manufacturing, product development, and marketing of any products resulting from the agreement. The Company received a $2 million non‑refundable upfront payment from Roche upon execution of the agreement. The Company is also entitled to receive up to a total of $44 million in milestone payments, plus royalties on the commercial sales of Kadcyla or any other resulting products. Total milestones are categorized as follows: development milestones—$13.5 million; and regulatory milestones—$30.5 million. Through December 31, 2018, the Company has received and recognized $13.5 million and $20.5 million in development and regulatory milestone payments, respectively, related to Kadcyla. The next potential milestone the Company will be entitled to receive will be a $5 million regulatory milestone for marketing approval of Kadcyla for a first extended indication as defined in the agreement. The Company receives royalty reports and payments related to sales of Kadcyla from Roche one quarter in arrears. In accordance with the Company’s revenue recognition policy, $32.2, $28.1, $12.9, and $25.3 million of non-cash royalties on net sales of Kadcyla were recorded and included in royalty revenue for the years ended December 31, 2018 and 2017, the six‑month period ended December 31, 2016, and the year ended June 30, 2016. Kadcyla sales occurring after January 1, 2015 are covered by a royalty purchase agreement whereby the associated cash, except for a residual tail, would have been remitted to Immunity Royalty Holdings, L.P, or IRH. In January 2019, the Company announced the sale of its residual tail to OMERS, the defined benefit pension plan for municipal employees in the Province of Ontario, Canada, for $65.2 million, net of fees, as discussed further in Note F. Simultaneously, OMERS purchased IRH’s right to the royalties the Company previously sold as described above, therefore obtaining the rights to 100% of the royalties received from that date on. Roche, through its Genentech unit, also has licenses for the exclusive right to use the Company’s maytansinoid ADC technology with antibodies to four undisclosed targets, which were granted under the terms of a separate, now expired, 2000 right‑to‑test agreement with Genentech. For each of these licenses the Company received a $1 million license fee and is entitled to receive up to a total of $38 million in milestone payments and also royalties on the sales of any resulting products. The total milestones are categorized as follows: development milestones—$8 million; regulatory milestones—$20 million; and sales milestones—$10 million. The Company has not received any milestone payments from these agreements through December 31, 2018. Roche is responsible for the development, manufacturing, and marketing of any products resulting from these licenses. The next potential milestone the Company will be entitled to receive under any of these agreements will be a development milestone for filing of an IND application which will result in a $1 million payment being due. Amgen/Oxford BioTherapeutics Under a now‑expired right‑to‑test agreement established in 2000, the Company granted Amgen three exclusive development and commercialization licenses, for which the Company received an exercise fee of $1 million for each license taken. In May 2013, the Company granted Amgen one non‑exclusive development and commercialization license, for which the Company received an exercise fee of $500,000. In October 2013, the non‑exclusive license was amended and converted to an exclusive license, for which Amgen paid an additional $500,000 fee to the Company. Amgen has sublicensed its rights under this license to Oxford BioTherapeutics Ltd. (OBT). In December 2015, Amgen advised the Company that it had discontinued development of two product candidates, AMG 595 and AMG 172 that had been covered by two of Amgen’s four exclusive licenses, and in February 2016, Amgen subsequently terminated these two licenses. In August 2018, Amgen terminated one of its two remaining development and commercialization licenses leaving the sublicensed license as the last remaining license. As a result, the Company recorded the remaining $84,000 balance of the upfront payment that had been allocated to future performance obligations under this license as revenue, which is included in license and milestone fees for the year ended December 31, 2018. For the remaining development and commercialization license, the Company is entitled to receive up to a total of $34 million in milestone payments, plus royalties on the commercial sales of any resulting products. The total milestones are categorized as follows: development milestones—$9 million; regulatory milestones—$20 million; and sales milestones—$5 million. Amgen (or its sublicensee(s)) is responsible for the manufacturing, development, and marketing of any products resulting from this development and commercialization license. Through December 31, 2018, the Company has received and recognized an aggregate of $4 million in milestone payments for compounds covered under this agreement now or in the past. In September 2015, Amgen’s IND under the then remaining license not sublicensed to Oxford BioTherapeutics became effective, triggering a $1 million milestone payment to the Company which is included in license and milestone fee revenue for the year ended June 30, 2016. In December 2018, an IND filed by OBT was accepted, triggering a $1 million milestone payment to the Company. The next potential milestone the Company will be entitled to receive under the remaining license will be a development milestone for the first dosing of a patient in a U.S. Phase II clinical trial, which will result in a $3 million payment being due. Costs directly attributable to the Amgen collaborative agreement are comprised of compensation and benefits related to employees who provided research and development services on behalf of Amgen as well as costs of clinical materials sold. Indirect costs are not identified to individual collaborators. The costs related to the research and development services amounted to $15,000 for fiscal year 2016. There were no similar costs recorded after fiscal year 2016. Sanofi In 2003, the Company entered into a broad collaboration agreement with Sanofi (formerly Aventis Pharmaceuticals) to discover, develop and commercialize antibody‑based products. The collaboration agreement provided Sanofi with worldwide development and commercialization rights to new antibody‑based products directed to targets that are included in the collaboration, including the exclusive right to use the Company’s maytansinoid ADC technology in the creation of products developed to these targets. Through December 31, 2018, the Company recognized an aggregate of $26.5 million in development milestone payments for compounds covered under this agreement now or in the past, including $6 million of milestone payments received and included in license and milestone fee revenue for the year ended December 31, 2017. In May 2017, the Company and an affiliate of Sanofi amended the license agreements covering all compounds in development by Sanofi using the Company’s technology. Under the terms of the amended 2003 collaboration and license agreement, the Company granted Sanofi a fully-paid, exclusive license to develop, manufacture, and commercialize four experimental compounds in development. The Company also amended a separate 2013 exclusive license entered into pursuant to a separate, now-expired right-to-test agreement to grant Sanofi a fully-paid, exclusive license to develop, manufacture and commercialize another experimental compound being studied for the treatment of solid tumors. As consideration for these amendments, the Company received a $30 million payment and agreed to forego a limited co-promotion option in the U.S. with respect to the compounds covered by the 2003 agreement, as well as future milestones or royalties with respect to all licensed products. In accordance with ASC-605-25, the Company determined that there were no remaining deliverables upon execution of the amendments, and accordingly, the $30 million was recognized as revenue and is included in license and milestone fee revenue for the year ended December 31, 2017. Biotest In 2006, the Company granted Biotest an exclusive development and commercialization license to our maytansinoid ADC technology for use with antibodies that target CD138. The product candidate indatuximab ravtansine is in development under this agreement. Biotest is responsible for the manufacturing, development, and marketing of any products resulting from the agreement. The Company received a $1 million upfront payment upon execution of the agreement and could receive up to $35.5 million in milestone payments, as well as royalties on the commercial sales of any resulting products. The total milestones are categorized as follows: development milestones—$4.5 million; and regulatory milestones—$31 million. In September 2008, Biotest began Phase I evaluation of indatuximab ravtansine which triggered a $500,000 milestone payment to the Company. The next potential milestone the Company will be entitled to receive will be a development milestone for commencement of a Phase IIb clinical trial (as defined in the agreement) which will result in a $2 million payment being due. Costs directly attributable to the Biotest collaborative agreement are comprised of compensation and benefits related to employees who provided research and development services on behalf of Biotest as well as costs of clinical materials sold. Indirect costs are not identified to individual collaborators. The costs related to the research and development services amounted to $50,000, $41,000, $22,000, and $160,000 for the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and fiscal year 2016, respectively. The costs related to clinical materials sold were $549,000 and $1.8 million for the six months ended December 31, 2016 and fiscal year 2016, respectively. There were no costs related to clinical materials sold for any subsequent periods. Bayer In 2008, the Company granted Bayer an exclusive development and commercialization license to the Company’s maytansinoid ADC technology for use with antibodies or other proteins that target mesothelin. Bayer HealthCare is responsible for the research, development, manufacturing, and marketing of any products resulting from the license. The Company received a $4 million upfront payment upon execution of the agreement which was recognized as revenue ratably over the Company’s estimated period of substantial involvement which concluded in September 2012. For each compound developed and marketed by Bayer under this collaboration the Company is entitled to receive a total of $170.5 million in milestone payments, plus tiered royalties between 4 - 7% on the commercial sales of any resulting products. The total milestones are categorized as follows: development milestones—$16 million; regulatory milestones—$44.5 million; and sales milestones—$110 million. Through December 31, 2018, the Company has received and recognized an aggregate of $13 million in milestone payments under this agreement. In January 2016, Bayer initiated a Phase II clinical study designed to support registration of its ADC product candidate, anetumab ravtansine, triggering a $10 million development milestone payment to the Company which is included in license and milestone fee revenue for the year ended June 30, 2016. In July 2017, Bayer announced that its Phase II clinical study did not meet its primary endpoint of progression-free survival. The safety and tolerability of anetumab ravtansine were consistent with earlier clinical findings and Bayer is continuing development in additional studies, including a Phase 1b multi-indication study in six different types of advanced solid tumors, and a Phase 1b combination-study in patients with recurrent platinum-resistant ovarian cancer. The next potential milestone the Company will be entitled to receive will be either a development milestone for commencement of a pivotal clinical trial for a second indication for anetumab ravtansine which will result in a $2 million payment being due or a regulatory milestone for filing of regulatory approval for its first indication for anetumab ravtansine which will result in a $6 million payment being due. Novartis The Company granted Novartis exclusive development and commercialization licenses to the Company’s maytansinoid and IGN ADC technology for use with antibodies to six specified targets under a now-expired right-to-test agreement established in 2010. The Company received a $45 million upfront payment in connection with the execution of the right‑to‑test agreement in 2010, and for each development and commercialization license taken for a specific target, the Company received an exercise fee of $1 million and is entitled to receive up to a total of $199.5 million in milestone payments, plus royalties on the commercial sales of any resulting products. The total milestones are categorized as follows: development milestones—$22.5 million; regulatory milestones—$77 million; and sales milestones—$100 million. The initial three-year term of the right-to-test agreement was extended by Novartis in October 2013 for an additional one-year period by payment of a $5 million fee to the Company. The Company also is entitled to receive payments for research and development activities performed on behalf of Novartis. Novartis is responsible for the manufacturing, development, and marketing of any products resulting from this agreement. In March 2013, the Company and Novartis amended the right‑to‑test agreement so that Novartis could take a license to develop and commercialize products directed at two undisclosed, related targets, one target licensed on an exclusive basis and the other target initially licensed on a non‑exclusive basis. The target licensed on a non‑exclusive basis may no longer be converted to an exclusive target due to the expiration of the right-to-test agreement. The Company received a $3.5 million fee in connection with the execution of the amendment to the agreement. In connection with the amendment, in March 2013, the Company granted Novartis the license referenced above under the right‑to‑test agreement, as amended, enabling it to develop and commercialize products directed at the two targets. The Company received a $1 million upfront fee with the execution of this license. In May 2018, Novartis terminated the license. As a result, the Company recorded the remaining $978,000 balance of the upfront payment that had been allocated to future performance obligations under this license as revenue, which is included in license and milestone fees for the year ended December 31, 2018. In October 2013 and November 2013, the Company granted Novartis its second and third exclusive licenses to single targets, and in October 2014, the three remaining exclusive licenses, each triggering a $1 million upfront payment to the Company and the opportunity to receive milestone payments totaling $199.5 million, as outlined above, plus royalties on the commercial sales of any resulting products. In January 2015 and May 2015, Novartis initiated Phase I, first-in-human clinical testing of its cKit-targeting ADC product candidate, LOP628, and P-cadherin-targeting ADC product candidate, PCA062, respectively, triggering a $5 million development milestone payment to the Company with each event. Novartis later discontinued clinical testing of LOP628. In December 2016, Novartis initiated Phase I, first-in-human clinical testing of its CDH6-targeting ADC product candidate, HKT288, triggering a $5 million milestone payment which the Company received in 2017. The next payment the Company could receive would be either a $7.5 million development milestone for commencement of a Phase II clinical trial under these three licenses or a $5 million development milestone for commencement of a Phase I clinical trial under one of its other two licenses. Costs directly attributable to the Novartis collaborative agreement are comprised of compensation and benefits related to employees who provided research and development services on behalf of Novartis as well as costs of clinical materials sold. Indirect costs are not identified to individual collaborators. The costs related to the research and development services amounted to $32,000, $17,000, and $67,000 for the year ended December 31, 2017, the six months ended December 31, 2016, and fiscal year 2016, respectively. There were no similar costs recorded in the year ended December 31, 2018. Lilly The Company granted Eli Lilly and Company (Lilly) three exclusive development and commercialization licenses under a now-expired right-to-test agreement established in 2011. The Company received a $20 million upfront payment in connection with the execution of the right‑to‑test agreement in 2011. Under the terms of this right-to-test agreement, the first license had no associated exercise fee, and the second and third licenses each had a $2 million exercise fee. The first development and commercialization license was granted in August 2013 and the agreement was amended in December 2013 to provide Lilly with an extension provision and retrospectively include a $2 million exercise fee for the first license in lieu of the fee due for either the second or third license. The second and third licenses were granted in December 2014, with one including the $2 million exercise fee and the other not. In September 2015, Lilly began Phase I evaluation of one of its licensed ADC products which triggered a $5 million milestone payment to the Company which is included in license and milestone fee revenue for the fiscal year ended June 30, 2016. In October 2018, Lilly terminated its three development and commercialization licenses. As a result, the Company recorded the remaining $692,000 balance of the upfront payment that had been allocated to future performance obligations under this license as revenue, which is included in license and milestone fees for the year ended December 31, 2018. Costs directly attributable to the Lilly collaborative agreement are comprised of compensation and benefits related to employees who provided research and development services on behalf of Lilly as well as costs of clinical materials sold. Indirect costs are not identified to individual collaborators. The costs related to the research and development services amounted to $24,000, $74,000, $46,000, and $182,000 for the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and fiscal year 2016, respectively. The costs related to clinical materials sold were $1.2 million and $1.1 million for the year ended December 31, 2017 and fiscal year 2016, respectively. There were no similar costs recorded during the year ended December 31, 2018 and six months ended December 31, 2016. CytomX In 2016, the Company granted CytomX an exclusive development and commercialization license to the Company’s maytansinoid ADC technology for use with Probodies™ that target CD166 under a now expired reciprocal right-to-test agreement. The Company neither received nor made an upfront cash payment in connection with the execution of the right-to-test agreement or the license agreement. An amendment of the agreement executed simultaneously with the license, granted CytomX the right, for a specified period of time, to substitute the specified target with another as yet unspecified target. Accordingly, the revenue associated with this license was deferred until the expiration of that substitution right in January 2017, whereupon the Company recognized $12.7 million of the $13 million of arrangement consideration allocated to the development and commercialization license, which is included in license and milestone fee revenue for the year ended December 31, 2017. With respect to the development and commercialization license granted to CytomX, the Company is entitled to receive up to a total of $160 million in milestone payments plus royalties on the commercial sales of any resulting product. The total milestones are categorized as follows: development milestones—$10 million; regulatory milestones—$50 million; and sales milestones—$100 million. In June 2017, CytomX enrolled its first patient in a Phase 1 clinical trial for its product candidate, CX-2009, triggering a $1 million development milestone payment which is included in license and milestone fee revenue for the year ended December 31, 2017. Assuming no annual maintenance fee is payable as described below, the next payment the Company could receive would be a $3 million development milestone payment with commencement of a Phase II clinical trial. CytomX is responsible for the manufacturing, development, and marketing of any products resulting from the development and commercialization license taken by CytomX under this collaboration. In 2017, we took exclusive development and commercialization licenses to CytomX’s proprietary antibody-masking (Probody) technology for use with Probodies that target two specified targets under the same reciprocal right-to-test agreement. We terminated one of these licenses for convenience prior to the end of 2017. No upfront cash payments were made by the Company with the execution of these license agreements. With respect to the remaining license, the Company will potentially be required to pay up to a total of $80 million in milestone payments, plus royalties on the commercial sales of any resulting product. The total milestones per license are categorized as follows: development milestones—$7 million; regulatory milestones—$23 million; and sales milestones—$50 million. Assuming no annual maintenance fee is payable as described below, the next payment the Company could be required to make is a $1 million development milestone payment with commencement of a Phase I clinical trial. The Company is responsible for the manufacturing, development and marketing of any products resulting from any development and commercialization license taken by the Company under this collaboration. In addition, each party may be liable to pay annual maintenance fees to the other party if the licensed product candidate covered under each development and commercialization license has not progressed to a specified stage of development within a specified time frame. The arrangement was accounted for based on the fair value of the items exchanged. The items to be delivered to CytomX under the arrangement are accounted for under the Company’s revenue recognition policy. The items to be received from CytomX are recorded as research and development expenses as incurred. Costs directly attributable to the CytomX collaborative agreement are comprised of compensation and benefits related to employees who provided research and development services on behalf of CytomX as well as costs of clinical materials sold. Indirect costs are not identified to individual collaborators. The costs related to the research and development services amounted to $195,000, $256,000, $427,000, and $868,000 for the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and for fiscal year 2016, respectively. The costs related to clinical materials sold were $3.5 million and $1.0 million for the years ended December 31, 2018 and 2017, respectively. There were no similar costs recorded during the six months ended December 31, 2016 and fiscal year 2016. Takeda In March 2015, the Company entered into a three-year right-to-test agreement with Takeda Pharmaceutical Company Limited (Takeda) through its wholly owned subsidiary, Millennium Pharmaceuticals, Inc. The agreement provides Takeda with the right to (a) take exclusive options, with certain restrictions, to individual targets selected by Takeda for specified option periods, (b) test the Company’s ADC technology with Takeda’s antibodies directed to the targets optioned under a right-to-test, or research, license, and (c) take exclusive licenses to use the Company’s ADC technology to develop and commercialize products to targets optioned for up to two individual targets on terms specified in the right-to-test agreement by the end of the term of the right-to-test agreement, after which any then outstanding options would lapse. Takeda had the right to extend the three-year right-to-test period for one additional year by payment to the Company of $4 million. Alternatively, Takeda had the right to expand the scope of the right-to-test agreement by payment to the Company of $8 million. Takeda is responsible for the manufacturing, development, and marketing of any products resulting from this collaboration. The Company received a $20 million upfront payment in connection with the execution of the right-to-test agreement and, for each development and commercialization license taken, is entitled to receive up to a total of $210 million in milestone payments, plus royalties on the commercial sales of any resulting products. The total milestones are categorized as follows: development milestones—$30 million; regulatory milestones—$85 million; and sales milestones—$95 million. The Company also is entitled to receive payments for delivery of cytotoxic agents to Takeda and research and development activities performed on behalf of Takeda. A first license was granted to Takeda in December 2015, and as a result, the Company recognized $8.6 million of the arrangement consideration allocated to the development and commercialization licenses, which is included in license and milestone fee revenue for the year ended June 30, 2016. With this first development and commercialization license taken, the amount of the arrangement consideration allocated to future technological improvements commenced to be recognized as revenue ratably over the period the Company is obligated to make available any technological improvements, which is the equivalent to the estimated term of the license. The Company estimates the term of a development and commercialization license to be approximately 25 years, which reflects management’s estimate of the time necessary to develop and commercialize therapeutic products pursuant to the license plus the estimated royalty term. The Company will reassess the estimated term at each subsequent reporting period. In March 2018, the right-to-test agreement expired without Takeda exercising its option to a second license or extending the agreement or expanding the agreement as it had the right to do for a third license. Accordingly, the remaining $10.9 million of revenue that had been deferred for such performance obligations was recognized as revenue and is included in license and milestone fees for the year ended December 31, 2018. In May 2018, Takeda enrolled its first patient in a Phase I clinical trial, triggering a $5 million milestone payment to the Company. Due to the likelihood of this milestone being attained, this milestone was recognized as a contract asset as part of the cumulative adjustment to transition to ASC 606. It had been previously allocated to the delivered license and the right to technological improvements. The next potential milestone payment the Company will be entitled to receive will be a $10 million development milestone payment with the initiation of a Phase II clinical trial. Takeda is responsible for the manufacturing, product development, and marketing of any products resulting from the remaining license. Costs directly attributable to the Takeda collaborative agreement are comprised of compensation and benefits related to employees who provided research and development services on behalf of Takeda. Indirect costs are not identified to individual collaborators. The costs related to the research and development services amounted to $199,000, $913,000, $678,000, and $469,000 for the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and for fiscal year 2016, respectively. The costs related to clinical materials sold were $650,000 and $2.1 million for the years ended December 31, 2018 and 2017, respectively. There were no similar costs recorded during the six months ended December 31, 2016 and fiscal year 2016. Fusion In December 2016, the Company entered into an exclusive license agreement to a specified target with Fusion Pharmaceuticals Inc. The Company is entitled to receive up to a total of $50 million in milestone payments, plus royalties on the commercial sales of any resulting products. The total milestones are categorized as follows: development milestones—$15 million; and sales milestones—$35 million. During the year ended December 31, 2018, a development milestone related to dosing of a first patient in a Phase I clinical trial became probable of being attained, which resulted in a $500,000 contract asset and the related license and milestone fee revenue being recorded in the current period. The next potential milestone payment the Company will be entitled to receive will be a $1.5 million development milestone payment with the initiation of a Phase II clinical trial. Fusion is responsible for the manufacturing, development, and marketing of any products resulting from the license. Debiopharm In May 2017, Debiopharm International SA (Debiopharm) acquired the Company’s IMGN529 program, a clinical-stage anti-CD37 ADC for the treatment of patients with B-cell malignancies, such as non-Hodgkin lymphomas (NHL). Under the terms of the Exclusive License and Asset Purchase agreement, the Company received a $25 million upfront payment for specified assets related to IMGN529 and a paid-up license to the Company’s ADC technology and a $5 million milestone payment upon substantial completion of the transfer of ImmunoGen technologies related to the program (technology transfer), which was completed in the fourth quarter of 2017. $4.5 million was received for this milestone in December 2017, and the balance in January 2018 upon delivery of the final materials related to the transfer. Accordingly, the Company recorded $500,000 and $29.5 million of license and milestone fee revenue in 2018 and 2017, respectively. In addition, ImmunoGen is eligible for a second success-based milestone payment of $25 million upon IMGN529 entering a Phase 3 clinical trial. The milestone payment will be significantly reduced if a Phase 3 trial using the Company’s technology but not the IMGN529 antibody commences prior to IMGN529 entering a Phase 3 trial. The Company does not believe this scenario is likely to occur. Costs directly attributable to the Debiopharm agreement are comprised of compensation and benefits related to employees who provided research and development services on behalf of Debiopharm. Indirect costs are not identified to individual collaborators. The costs related to the research and development services amounted to $99,000 for the year ended December 31, 2018. There were no similar costs recorded in prior periods. Jazz Pharmaceuticals In August 2017, the Company entered into a collaboration and option agreement with Jazz Pharmaceuticals Ireland Limited (Jazz), a subsidiary of Jazz Pharmaceuticals plc, granting Jazz exclusive, worldwide rights to opt into development and commercialization of two early-stage, hematology-related ADC programs, as well as an additional program to be designated during the term of the agreement. The programs covered under the agreement include IMGN779, a CD33-targeted ADC for the treatment of acute myeloid leukemia (AML) in Phase 1 testing, IMGN632, a CD123-targeted ADC for hematological malignancies also in Phase 1 testing, and an early-stage program to be determined at a later date. Under the terms of the agreement, the Company will be generally responsible for the development of the three ADC programs prior to any potential opt-in by Jazz. Following any opt-in, Jazz would be generally r

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2018
Property and Equipment
Property and Equipment	D. Property and Equipment Property and equipment consisted of the following at December 31, 2018 and 2017 (in thousands): December 31, December 31, 2018 2017 Leasehold improvements $ 20,684 $ 36,460 Machinery and equipment 22,558 23,123 Computer hardware and software 5,494 8,273 Furniture and fixtures 3,546 3,710 Assets under construction 113 416 $ 52,395 $ 71,982 Less accumulated depreciation (39,504) (57,444) Property and equipment, net $ 12,891 $ 14,538 Depreciation expense was $7.4, $6.0, $3.1, and $5.3 million for the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and for the year ended June 30, 2016, respectively. Included in the table above, the Company’s investment in equipment under capital leases was $595,000 and $449,000, net of accumulated amortization of $684,000 and $479,000, at December 31, 2018 and 2017, respectively.

Convertible 4.5% Senior Notes

Convertible 4.5% Senior Notes	12 Months Ended
	Dec. 31, 2018
Convertible 4.5% Senior Notes
Convertible 4.5% Senior Notes	E. Convertible 4.5% Senior Notes In 2016, the Company issued Convertible 4.5% Senior Notes with an aggregate principal amount of $100 million. The Company received net proceeds of $96.6 million from the sale of the Convertible Notes, after deducting fees and expenses of $3.4 million. During the second half of calendar 2017, the Company entered into privately negotiated exchange agreements with a number of holders of our outstanding Convertible Notes, pursuant to which the Company agreed to exchange, in a private placement, $97.9 million in aggregate principal amount of Convertible Notes held by the holders for 26,160,187 newly issued shares of our common stock, equivalent to the number of shares based on the original conversion terms, plus an additional number of newly issued shares of common stock determined based on the volume-weighted average trading price of the common stock over certain trading days. As a result of the agreements, 2,784,870 additional shares were issued. In accordance with ASC, Topic 470-20, “Debt – Debt with Conversion and Other Options,” based on the short period of time the conversion offer was open and the substantive conversion feature offer, the Company accounted for the conversion of $96.9 million of the debt as an inducement by expensing the fair value of the shares that were issued in excess of the original terms of the Convertible Notes. Due to the passage of time between the inducement offer and execution of the agreement, the Company accounted for the conversion of the other $1 million of the debt as an extinguishment by expensing the fair value of the shares that were issued in excess of net book value of the Convertible Notes. As a result, the Company recorded a non-cash debt conversion expense in the amount of $22.9 million in the year ended December 31, 2017. In addition, accrued interest on the bonds of $743,000 which the noteholders forfeited, $2.5 million of deferred financing costs and $1.7 million in transaction costs were charged to paid-in capital as a result of the issuance of common stock upon conversion. The remaining $2.1 million of Convertible Notes are governed by the terms of an indenture between the Company, as issuer, and Wilmington Trust, National Association, as the trustee. The Convertible Notes are senior unsecured obligations and bear interest at a rate of 4.5% per year, payable semi-annually in arrears on January 1 and July 1 of each year, commencing on January 1, 2017. The Company recorded $95,000, $3.0 million, $2.2 million and $138,000 of interest expense in the years ended December 31, 2018 and 2017, the six months ended December 31, 2016 and the year ended June 30, 2016, respectively. The Convertible Notes will mature on July 1, 2021, unless earlier repurchased or converted. Holders may convert their notes at their option at any time prior to the close of business on the business day immediately preceding the stated maturity date. Upon conversion, the Company will deliver for each $1,000 principal amount of converted notes a number of shares equal to the conversion rate, which will initially be 238.7775 shares of common stock, equivalent to an initial conversion price of approximately $4.19. The conversion rate will be subject to adjustment in some circumstances, but will not be adjusted for any accrued and unpaid interest. The Company analyzed the terms of the Convertible Notes and determined that under current accounting guidance the notes would be entirely accounted for as debt and none of the terms of the notes require separate accounting. As part of the issuance of the Convertible Notes, the Company incurred $3.4 million of transaction costs, of which $2.5 million was reclassed to equity upon conversion noted above. The remaining net unamortized balance of $50,000 was netted against the Convertible Notes in the accompanying consolidated balance sheet and is being amortized to interest expense ratably over the term of the Convertible Notes.

Liability Related to Sale of Fu

Liability Related to Sale of Future Royalties	12 Months Ended
	Dec. 31, 2018
Liability Related to Sale of Future Royalties
Liability Related to Sale of Future Royalties	F. Liability Related to Sale of Future Royalties In 2015, IRH purchased the right to receive 100% of the royalty payments on commercial sales of Kadcyla arising under the Company’s development and commercialization license with Genentech, until IRH had received aggregate royalties equal to $235 million or $260 million, depending on when the aggregate royalties received by IRH reached a specified milestone. Once the applicable threshold was met, if ever, the Company would thereafter have received 85% and IRH would have received 15% of the Kadcyla royalties for the remaining royalty term. At consummation of the transaction the Company received cash proceeds of $200 million. As part of this sale, the Company incurred $5.9 million of transaction costs, which are presented net of the liability in the accompanying consolidated balance sheet and are being amortized to interest expense over the estimated life of the royalty purchase agreement. Although the Company sold its rights to receive royalties from the sales of Kadcyla, as a result of its ongoing involvement in the cash flows related to these royalties, the Company will continue to account for these royalties as revenue and recorded the $200 million in proceeds from this transaction as a liability related to sale of future royalties (Royalty Obligation) that will be amortized using the interest method over the estimated life of the royalty purchase agreement. In January 2019, the Company sold its residual rights to receive royalty payments on commercial sales of Kadcyla to OMERS, the defined benefit pension plan for municipal employees in the Province of Ontario, Canada, for $65.2 million, net of fees. Simultaneously, OMERS purchased IRH’s right to the royalties the Company previously sold as described above, therefore obtaining the rights to 100% of the royalties received from that date on. The following table shows the activity within the liability account during the year ended December 31, 2018 and the period from inception (in thousands): Twelve Months Period from Ended inception to December 31, December 31, 2018 2018 Liability related to sale of future royalties, net — beginning balance $ 169,413 $ — Proceeds from sale of future royalties, net — 194,135 Kadcyla royalty payments received and paid (31,805) (103,624) Non-cash interest expense recognized 10,617 57,714 Liability related to sale of future royalties, net — ending balance $ 148,225 $ 148,225 As royalties are remitted to IRH and subsequently OMERS, the balance of the Royalty Obligation will be effectively repaid over the life of the agreement. In order to determine the amortization of the Royalty Obligation, the Company is required to estimate the total amount of future royalty payments to be received and remitted as noted above over the life of the agreement. The sum of these amounts less the $200 million proceeds the Company received will be recorded as interest expense over the life of the Royalty Obligation. Since inception, the Company’s estimate of this total interest expense resulted in an effective annual interest rate of 7.2% and a current effective interest rate of 5.7% as of December 31, 2018. The Company periodically assesses the estimated royalty payments to IRH/OMERS and to the extent such payments are greater or less than its initial estimates, or the timing of such payments is materially different than its original estimates, the Company will prospectively adjust the amortization of the Royalty Obligation. There are a number of factors that could materially affect the amount and timing of royalty payments from Genentech, most of which are not within the Company’s control. Such factors include, but are not limited to, changing standards of care, the introduction of competing products, manufacturing or other delays, biosimilar competition, patent protection, adverse events that result in governmental health authority imposed restrictions on the use of the drug products, significant changes in foreign exchange rates as the royalties remitted to IRH/OMERS are made in U.S. dollars (USD) while significant portions of the underlying sales of Kadcyla are made in currencies other than USD, and other events or circumstances that could result in reduced royalty payments from Kadcyla, all of which would result in a reduction of non-cash royalty revenues and the non-cash interest expense over the life of the Royalty Obligation. Conversely, if sales of Kadcyla are more than expected, the non-cash royalty revenues and the non-cash interest expense recorded by the Company would be greater over the term of the Royalty Obligation. In addition, the royalty purchase agreement grants IRH/OMERS the right to receive certain reports and other information relating to the royalties and contains other representations and warranties, covenants and indemnification obligations that are customary for a transaction of this nature.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Taxes
Income Taxes	G. Income Taxes The difference between the Company’s expected tax benefit, as computed by applying the applicable U.S. federal corporate tax rate to loss before the benefit for income taxes, and actual tax is reconciled in the following chart (in thousands): Six Months Ended Year Ended Years Ended December 31, December 31, June 30, 2018 2017 2016 2016 Loss before income tax expense $ (168,843) $ (96,012) $ (78,883) $ (144,817) Expected tax benefit at 21%, 34%, 34% and 34%, respectively $ (35,457) $ (32,644) $ (26,820) $ (49,238) Permanent differences (103) 25 15 345 Incentive stock options 1,144 1,528 1,313 2,501 State tax benefit net of federal benefit (10,622) (3,537) (4,157) (7,954) Change in valuation allowance, net 53,706 (63,238) 32,922 62,505 Federal research credit (2,466) (2,204) (1,232) (4,109) Federal orphan drug credit (6,934) (7,118) (2,901) (4,241) Expired loss and credit carryforwards — — — 184 Change in U.S. tax law — 97,479 — — Debt inducement — 8,044 — — Lease incentive 109 — — — Stock option expirations 623 1,665 860 7 Benefit for income taxes $ — $ — $ — $ — At December 31, 2018, the Company has net operating loss, or NOL, carryforwards of $665.6 million available to reduce federal taxable income, if any, that begin to expire in 2028 through 2037 and $194.0 million of the federal NOL carryforwards can be carried forward indefinitely. The Company has $501.1 million of NOL carryforwards available to reduce state taxable income, if any, that expire in 2033 through 2038. The Company also has federal and state credit carryforwards of $59.4 million and $13.0 million, respectively, available to offset federal and state income taxes, which expire beginning in 2019. Due to the degree of uncertainty related to the ultimate use of the loss carryforwards and tax credits, the Company has established a valuation allowance to fully reserve these tax benefits. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets and liabilities as of December 31, 2018 and 2017 are as follows (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 171,437 $ 118,672 Research and development tax credit carryforwards 69,710 58,606 Property and other intangible assets 297 2,272 Deferred revenue 22,075 25,997 Stock-based compensation 12,849 12,125 Deferred lease incentive 2,639 2,889 Other liabilities 2,920 3,037 Royalty sale 38,593 47,143 Total deferred tax assets $ 320,520 $ 270,741 Deferred tax liabilities: Stock-based compensation (156) — Royalty sale transaction costs (625) (859) Total deferred tax liabilities $ (781) $ (859) Valuation allowance (319,739) (269,882) Net deferred tax assets/(liabilities) $ — $ — The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. As required by the provisions of ASC 740, the Company has determined that it is not more-likely-than-not that the tax benefits related to the federal and state deferred tax assets will be realized for financial reporting purposes. Accordingly, the deferred tax assets have been fully reserved at December 31, 2018 and 2017. The valuation allowance increased by $49.9 million during the year ended December 31, 2018 due primarily to additional net loss incurred during the year. In December 2017, the Tax Cuts and Jobs Act, or the Tax Act (“TCJA”), was signed into law. Among other things, the Tax Act permanently lowers the corporate federal income tax rate to 21% from the existing maximum rate of 35%, effective for tax years including or commencing January 1, 2018. As a result of the reduction of the corporate federal income tax rate to 21%, U.S. GAAP requires companies to revalue their deferred tax assets and deferred tax liabilities as of the date of enactment, with the resulting tax effects accounted for in the reporting period of enactment. For 2017, this revaluation resulted in a provision of $97.5 million to income tax expense in continuing operations and a corresponding reduction in the valuation allowance. As a result, there was no impact to the Company’s income statement as a result of the reduction in tax rates. The other provisions of the TCJA did not have a material impact on the consolidated financial statements. Utilization of the NOL and credit carryforwards may be subject to a substantial annual limitation due to ownership change limitations that have occurred previously or that could occur in the future as provided by Section 382 of the Internal Revenue Code of 1986, as well as similar state and foreign provisions. These ownership changes may limit the amount of NOL and credit carry forwards that can be utilized annually to offset future taxable income and tax, respectively. 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 percentage points over a three‑year period. Since the Company’s formation, it has raised capital through the issuance of capital stock on several occasions (both pre and post initial public offering) which, combined with the purchasing shareholders’ subsequent disposition of those shares, may have resulted in a change of control, as defined by Section 382, or could result in a change of control in the future upon subsequent disposition. During fiscal year 2015, the Company completed a study to assess whether a change of control has occurred or whether there have been multiple changes of control since its formation and determined no ownership change occurred under Section 382. The study has not been updated beyond fiscal year 2015. Additionally, the Company has not completed a detailed Research and Development Credit Study (including the Orphan Drug Credit); accordingly, it is probable that a portion of the tax credit carryforward may not be available to offset future income. The Company accounts for uncertain tax positions under the recognition and measurement criteria of ASC 740-10. For those tax positions for which it is more likely than not that a tax benefit will be sustained, the Company records the largest amount of tax benefit with a greater than 50% likelihood of being realized upon settlement with a taxing authority that has full knowledge of all relevant information. If the Company does not believe that it is not more likely than not that a tax benefit will be sustained, no tax benefit is recognized. As of December 31, 2018 and 2017, no uncertain tax positions have been recorded. Interest and penalties related to the settlement of uncertain tax positions, if any, will be reflected in income tax expense. The Company did not recognize any interest and penalties associated with unrecognized tax benefits in the accompanying consolidated financial statements. The Company does not expect any material changes to the unrecognized benefits within 12 months of the reporting date. Due to existence of the valuation allowance, future changes in the Company’s unrecognized tax benefits will not impact our effective tax rate. The statute of limitations for assessment by the Internal Revenue Service, or IRS, and state tax authorities is open for tax years ending after June 30, 2014, although carryforward attributes that were generated prior to fiscal year 2014 may still be adjusted upon examination by the IRS or state tax authorities if they either have been or will be used in a future period.

Capital Stock

Capital Stock	12 Months Ended
	Dec. 31, 2018
Capital Stock
Capital Stock	H. Capital Stock Common Stock Reserved At December 31, 2018, the Company has reserved 24.7 million shares of authorized common stock for the future issuance of shares under the 2006, 2016, and 2018 Plans. See “Stock‑Based Compensation” in Note B for a description of the 2018 Plan. Stock Options As of December 31, 2018, the 2018 Plan was the only employee share‑based compensation plan of the Company under which grants can be made. During the year ended December 31, 2018, holders of options issued under the option plans exercised their rights to acquire an aggregate of 742,000 shares of common stock at prices ranging from $1.84 to $12.21 per share. The total proceeds to the Company from these option exercises were $3.5 million. The Company granted options with an exercise price equal to the fair market value of the common stock on the date of such grant. The following options and their respective weighted‑average exercise prices per share were exercisable at December 31, 2018, 2017, and 2016, and June 30, 2016: Weighted‑ Exercisable Average (in thousands) Exercise Price December 31, 2018 8,405 $ 11.47 December 31, 2017 7,996 $ 12.16 December 31, 2016 7,898 $ 13.15 June 30, 2016 6,453 $ 12.63 2001 Non‑Employee Director Stock Plan In 2001, the Company’s shareholders approved the establishment of the 2001 Non‑Employee Director Stock Plan, or the 2001 Director Plan, and 50,000 shares of common stock to be reserved for grant thereunder. The 2001 Director Plan provided for the granting of awards to Non‑Employee Directors and, at the election of Non‑Employee Directors, to have all or a portion of their awards in the form of cash, stock, or stock units. All stock or stock units are immediately vested. The number of stock or stock units issued was determined by the market value of the Company’s common stock on the last date of the Company’s fiscal quarter for which the services are rendered. The 2001 Director Plan was administered by the Board of Directors which was authorized to interpret the provisions of the 2001 Director Plan, determine which Non‑Employee Directors would be granted awards, and determine the number of shares of stock for which a stock right will be granted. The 2001 Director Plan was replaced in 2004 by the 2004 Non‑Employee Director Compensation and Deferred Share Unit Plan. During the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and the fiscal year ended June 30, 2016, the Company recorded $31,000, $28,000, $(7,000), and $(72,000) in compensation expense (expense reduction), respectively, related to approximately 6,000 stock units outstanding under the 2001 Director Plan. The value of the stock units was adjusted to market value at each reporting period. A market value of $72,000 for the stock units was paid to a retiring director in June 2018, effectively terminating the plan. 2004 Non‑Employee Director Compensation and Deferred Share Unit Plan Under the 2004 Non-Employee Director Compensation and Deferred Share Unit Plan, or the 2004 Director Plan, as amended, between 2004 and 2009 non-employee directors were paid their annual retainers in the form of deferred stock units, based on the fair market value of the Company’s common stock on the last date of the Company’s fiscal year prior to the year for which services were rendered, and in cash, with the option, at their discretion, to have all or a portion of the cash portion paid in additional deferred stock units. All deferred stock units awarded under the 2004 Director Plan have vested, and are redeemed on the date a director ceases to be a member of the Board, at which time such director’s deferred stock units will be settled in shares of common stock of the Company issued under the 2006 Plan at a rate of one share for each vested. Compensation Policy for Non‑Employee Directors In September 2009, the Board adopted a new Compensation Policy for Non‑Employee Directors, which superseded the 2004 Plan and made certain changes to the compensation of its non‑employee directors. The Compensation Policy for Non-Employee Directors, as amended as recently as March 2018, consists of three elements: cash compensation; deferred stock units; and stock options. Cash Compensation Each non-employee director receives annual meeting fees which are paid in quarterly installments in, at each director’s election, either cash or deferred stock units. Deferred Stock Units Non-employee directors receive deferred stock units as follows:  New non-employee directors are initially awarded 8,000 deferred stock units (6,500 deferred stock units prior to March 28, 2018), with each unit relating to one share of the Company’s common stock. These awards vest quarterly over three years from the date of grant, contingent upon the individual remaining a director of the Company as of each vesting date.  Thereafter, non-employee directors are annually awarded 4,000 deferred stock units (3,000 deferred stock units prior to March 28, 2018). If a non-employee director is first elected to the Board other than at an annual meeting of shareholders, such non-employee director’s annual award of 4,000 deferred stock units will be pro-rated based on the number of days between his or her date of election and the date of grant of his or her first annual deferred stock unit award. These awards vest quarterly over approximately one year from the date of grant, contingent upon the individual remaining a director of the Company as of each vesting date. Vested deferred stock units are redeemed on the date a director ceases to be a member of the Board, at which time such director’s deferred stock units will generally be settled in shares of the Company’s common stock issued under our 2018 Plan (or its predecessor plans, depending on the grant date of the deferred stock units) at a rate of one share for each vested deferred stock unit then held. Any deferred stock units that remain unvested at that time will be forfeited. All unvested deferred stock units will automatically vest immediately prior to the occurrence of a change of control, as defined in the 2018 Plan (or the substantially identical definition in the predecessor plans, as applicable). Pursuant to the Compensation Policy for Non-Employee Directors, in June 2018, February 2018 and January 2017, the Company issued retiring directors 95,497, 77,012, and 53,248 shares of common stock of the Company to settle outstanding deferred share units. Pursuant to the Compensation Policy for Non‑Employee Directors, as amended, the Company recorded: · $361,000 in compensation expense during the year ended December 31, 2018 related to the grant of 46,000 deferred share units and 10,500 deferred share units previously granted; · $206,000 in compensation expense during the year ended December 31, 2017 related to the grant of 47,000 deferred share units and 12,000 deferred share units previously granted; · $215,000 in compensation expense during the six months ended December 31, 2016 related to the grant of 37,000 deferred share units and 12,000 deferred share units previously granted; · $380,000 in compensation expense during the year ended June 30, 2016 related to the grant of 41,000 deferred share units and 12,000 deferred share units previously granted; Stock Options Non-employee directors also receive stock option awards as follows:  Initial Stock Option Awards. Non-employee directors receive an initial stock option award covering 18,000 shares (10,000 shares prior to March 28, 2018) of our common stock on the date of his or her initial election or appointment to the Board, which is the grant date. These awards will have an exercise price equal to the market price of the Company’s stock on the grant date, will vest quarterly over a three-year period from the grant date, and will expire on the tenth anniversary of the grant date, contingent upon the individual remaining a director of the Company during such period.  Annual Stock Option Awards. Non-employee directors receive an annual stock option award covering 18,000 shares (10,000 shares prior to March 28, 2018) of our common stock on the date of our annual meeting of shareholders, which is the grant date. These awards will have an exercise price equal to the market price of the Company’s stock on the grant date, will vest quarterly over approximately one year from the grant date, and will expire on the tenth anniversary of the grant date, contingent upon the individual remaining a director of the Company during such period.  Off-Cycle Initial Awards. If a non-employee director is first elected to the Board other than at an annual meeting of shareholders, such non-employee director will receive an annual stock option award covering 18,000 shares (10,000 shares prior to March 28, 2018) of our common stock, pro-rated based on the number of days between his or her date of election and the date of grant of his or her first annual stock option award. These awards will have an exercise price equal to the market price of the Company’s stock on the date of grant, will vest quarterly over approximately one year from the grant date, and will expire on the tenth anniversary of the grant date, contingent upon the individual remaining a director of the Company during such period. All unvested stock option awards granted to non-employee directors will automatically vest immediately as of the date of a change of control, as defined in the 2018 Plan (or predecessor plans as applicable, which have substantially the identical terms). On December 9, 2016 the Board amended the Compensation Policy for Non-Employee Directors to create a transition period due to the change in the year-end. Effectively, one-half of the annual compensation awards described above were awarded to the directors on December 9, 2016 and a full-year’s compensation awarded on the date of the subsequent annual meetings. The directors received a total of 128,000 and 80,000 options in the years ended December 31, 2018 and 2017, 40,000 options in the six months ended December 31, 2016 and 80,000 options in the fiscal year ended June 30, 2016, and the related stock compensation expense is included in the amounts discussed in the “Stock‑Based Compensation” section of footnote B above.

Restructuring Charge

Restructuring Charge	12 Months Ended
	Dec. 31, 2018
Restructuring Charge
Restructuring Charge	I. Restructuring Charge In September 2016, the Board of Directors approved a plan to reengineer the business, resulting in a reduction of the workforce by approximately 17%, or 65 positions, which included the separation of 60 current employees. Communication of the plan to the impacted employees was substantially completed on September 29, 2016. All of the workforce reduction was completed as of December 31, 2016. As a result of the workforce reduction, in the six months ended December 31, 2016, the Company recorded a restructuring charge totaling $4.4 million related to termination benefits and other related charges, of which $2.8 million was recorded as a one-time termination benefit, and $593,000 recorded as a benefit under an ongoing benefit plan. The related cash payments initiated in October 2016 and were fully paid out by December 31, 2017. Additionally, approximately 762,000 stock options were forfeited in connection with the workforce reduction, and as a result, the Company recorded an approximate $837,000 credit to stock compensation expense which is included in research and development expense and general and administrative expense for the six months ended December 31, 2016. In addition to the termination benefits and other related charges, as a result of the September 2016 workforce reduction, the Company began seeking to sub-lease 10,281 square feet of unoccupied office space in Waltham that was leased in 2016. As of September 30, 2016, based on an estimate of the potential time it would take to find a tenant of approximately nine months, the anticipated sub-lease terms, and consideration of the tenant allowance that was given to the Company to build out the space, the Company determined it did not need to record a loss on the sub-lease. The Company also evaluated the balance of the leasehold improvements for potential impairment as of September 30, 2016. In performing the recoverability test, the Company concluded that a substantial portion of the leasehold improvements were not recoverable. The Company recorded an impairment charge of $970,000 related to these assets after comparing the fair value (using probability weighted scenarios with discounted cash flows) to the leasehold improvements’ carrying value, leaving a $193,000 remaining cost basis. During 2017, based on further evaluation of the prospects for sub-leasing the space, the Company determined that additional time would be required to find a tenant. Accordingly, the calculation for the potential sub-lease loss was updated and it was determined that the remaining balance of the leasehold improvements was impaired. Also, due to the additional time that is expected to secure a tenant, additional lease loss was recorded based on the change in estimate of the sub-lease assumption. The total of these charges in 2017 was $779,000. In February 2018, following an in-depth review of manufacturing and quality operations, the Board of Directors authorized management to implement a new operating model that will rely on external manufacturing and quality testing for drug substance and drug product for the Company’s development programs. The implementation of this new operating model led to the ramp-down of manufacturing and quality activities at the Norwood, Massachusetts facility during 2018, with a full decommissioning of the facility expected by early 2019. Implementation of the new operating model resulted in the separation of 22 employees. Communication of the plan to the affected employees was substantially completed on February 8, 2018. In connection with the implementation of the new operating model, the Company recorded a one-time charge of $1.2 million for severance in the first quarter related to a pre-existing plan. Additional expense was recorded for retention benefits over the remaining service period of the related employees, as well as marginal adjustments to severance resulting from voluntary terminations, which totaled $2.3 million. Additionally, certain options held by the employees to be separated were modified to extend the exercise period, resulting in a stock compensation charge of $157,000 in the first quarter. Cash payments related to severance will be substantially paid out by the end of the second quarter of 2019. The retention benefits were paid out in the fourth quarter of 2018. A summary of activity against the restructuring charge related to the employee terminations is as follows: Employee Termination Benefits Costs Initial charge related to employee benefits - March 2018 $ 1,189 Additional charges during the year 2,347 Payments during the period (2,695) Balance December 31, 2018 $ 841 II.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies
Commitments and Contingencies	J. Commitments and Contingencies Leases The Company currently has a lease agreement with CRP/King 830 Winter L.L.C. for the rental of approximately 120,000 square feet of laboratory and office space at 830 Winter Street, Waltham, MA through March 2026. The Company uses this space for its corporate headquarters and other operations. The Company may extend the lease for two additional terms of five years. Pursuant to lease amendments executed through December 2015, the Company received construction allowances totaling approximately $2 million to build out office and lab space to the Company’s specifications. The Company executed a fourth amendment to this lease in April 2018, leasing an additional 10,000 square feet of office space in order to accommodate employees being retained from the future Norwood closure previously discussed. The Company is entitled to a construction allowance of $400,000 to build normal tenant improvements in this space to its specifications. The Company began recording rent expense for this space during the quarter ending September 30, 2018, when it took control of the space for construction. The Company is required to pay certain operating expenses for the leased premises subject to escalation charges for certain expense increases over a base amount. In 2016, the Company entered into a lease agreement with PDM 930 Unit, LLC for the rental of 10,281 square feet of additional office space at 930 Winter Street, Waltham, MA through August 31, 2021. The Company received $617,000 as a construction allowance to build out the office space to the Company’s specifications. The Company is required to pay certain operating expenses for the leased premises based on its pro-rata share of such expenses for the entire rentable space of the building. The Company is actively seeking to sub-lease this space. The Company also leases 43,850 square feet of manufacturing and office space at 333 Providence Highway, Norwood, MA under an agreement through February 28, 2019. The Company is required to pay certain operating expenses for the leased premises subject to escalation charges for certain expense increases over a base amount. Effective in 2013, the Company entered into a lease agreement with River Ridge Limited Partnership for the rental of 7,507 square feet of additional office space at 100 River Ridge Drive, Norwood, MA. The initial term of the lease was for five years and two months commencing in July 2013 and the lease was terminated during 2018. Facilities rent expense, net of sublease income, was $7.7, $6.8, $3.5, and $6.5 million during the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and fiscal year 2016, respectively. As of December 31, 2018, the minimum rental commitments for the next five years and thereafter under the non‑cancelable operating lease agreements discussed above are as follows (in thousands): 2019 $ 5,498 2020 5,419 2021 5,257 2022 5,323 2023 5,450 Thereafter 12,336 Total minimum lease payments $ 39,283 In addition to the above table, the Company is responsible for variable operating costs and real estate taxes approximating $3.0 million per year through March 2026. There are no obligations under capital leases as of December 31, 2018, as all of the capital leases were single payment obligations which have all been made. Collaborations and Licenses The Company is contractually obligated to make potential future success‑based regulatory milestone payments in conjunction with certain collaborative agreements. These payments are contingent upon the occurrence of certain future events and, given the nature of these events, it is unclear when, if ever, the Company may be required to pay such amounts. Further, the timing of any future payment is not reasonably estimable. As of December 31, 2018, the maximum amount that may be payable in the future under the Company’s current collaborative agreements is $80 million. Manufacturing Commitments As of December 31, 2018, the Company has noncancelable obligations under several agreements related to in-process and future manufacturing of antibody and cytotoxic agents required for clinical supply of the Company’s product candidates totaling $1.3 million, all of which will be paid in calendar 2019. In the fourth quarter of 2018, the Company executed a commercial agreement, which superseded a previous letter agreement, with one of its manufacturers for future production of antibody through calendar 2022. Pursuant to the agreement, the Company’s noncancelable commitment is approximately €22 million at December 31, 2018. Litigation The Company is not party to any material litigation.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2018
Employee Benefit Plans
Employee Benefit Plans	K. Employee Benefit Plans The Company has a deferred compensation plan under Section 401(k) of the Internal Revenue Code (the 401(k) Plan). Under the 401(k) Plan, eligible employees are permitted to contribute, subject to certain limitations, up to 100% of their gross salary and the Company’s matching contribution is 50% of the first 6% of the eligible employees’ contributions. In the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and fiscal year 2016, the Company’s contributions to the 401(k) Plan totaled $1.0 million, $982,000, $536,000, and $1.1 million, respectively.

Quarterly Financial Information

Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information (Unaudited)
Quarterly Financial Information (Unaudited)	L. Quarterly Financial Information (Unaudited) Calendar Year 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, 2018 June 30, 2018 September 30, 2018 December 31, 2018 (In thousands, except per share data) Revenues: License and milestone fees $ 11,540 $ 1,321 $ 672 $ 1,747 Non-cash royalty revenue related to the sale of future royalties 7,190 7,242 8,441 9,281 Research and development support 383 388 388 218 Clinical materials revenue 702 336 1,427 2,170 Total revenues 19,815 9,287 10,928 13,416 Expenses: Research and development 44,831 38,701 47,243 43,681 General and administrative 9,995 8,652 8,347 9,752 Restructuring charge 1,731 686 870 406 Total expenses 56,557 48,039 56,460 53,839 Loss from operations (36,742) (38,752) (45,532) (40,423) Non-cash interest expense on liability related to sale of future royalty (3,046) (2,611) (2,546) (2,428) Interest expense on senior convertible notes (24) (23) (23) (25) Other (expense) income, net 1,199 (238) 1,294 1,077 Net loss $ (38,613) $ (41,624) $ (46,807) $ (41,799) Basic and diluted net loss per common share $ (0.30) $ (0.31) $ (0.32) $ (0.28) Calendar Year 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 (In thousands, except per share data) Revenues: License and milestone fees $ 18,730 $ 31,080 $ 79 $ 29,580 Royalty revenue — — — — Non-cash royalty revenue related to the sale of future royalties 7,613 6,439 6,503 7,587 Research and development support 1,478 902 650 452 Clinical materials revenue 678 599 1,248 1,829 Total revenues 28,499 39,020 8,480 39,448 Expenses: Research and development 32,888 35,319 31,689 39,843 General and administrative 8,119 8,836 7,908 9,048 Restructuring charge 386 — — 393 Total expenses 41,393 44,155 39,597 49,284 Loss from operations (12,894) (5,135) (31,117) (9,836) Non-cash interest expense on liability related to sale of future royalty and convertible senior notes (3,575) (3,501) (3,385) (3,221) Interest expense on senior convertible notes (1,125) (1,125) (762) (28) Non-cash debt conversion expense — — (22,191) (724) Other income, net 249 894 773 691 Net loss $ (17,345) $ (8,867) $ (56,682) $ (13,118) Basic and diluted net loss per common share $ $ $ $ Six Month Transition Period First Quarter Second Quarter Ended Ended September 30, 2016 December 31, 2016 (In thousands, except per share data) Revenues: License and milestone fees $ 76 $ 5,076 Royalty revenue — — Non-cash royalty revenue related to the sale of future royalties 6,184 6,710 Research and development support 1,354 1,427 Clinical materials revenue 46 633 Total revenues 7,660 13,846 Expenses: Research and development 32,909 33,657 General and administrative 9,459 8,536 Restructuring charge 4,130 301 Total expenses 46,498 42,494 Loss from operations (38,838) (28,648) Non-cash interest expense on liability related to sale of future royalty and convertible senior notes (5,018) (3,647) Interest expense on senior convertible notes (1,150) (1,099) Other income (expense), net 275 (758) Net loss $ (44,731) $ (34,152) Basic and diluted net loss per common share $ $ Fiscal Year 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended September 30, 2015 December 31, 2015 March 31, 2016 June 30, 2016 (In thousands, except per share data) Revenues: License and milestone fees $ 6,070 $ 10,692 $ 10,077 $ 76 Royalty revenue — 195 — — Non-cash royalty revenue related to the sale of future royalties 5,684 6,291 7,380 5,944 Research and development support 772 848 1,059 1,335 Clinical materials revenue 2,325 3 1,198 53 Total revenues 14,851 18,029 19,714 7,408 Expenses: Research and development 35,132 38,199 36,094 38,652 General and administrative 8,329 8,054 11,235 9,298 Total expenses 43,461 46,253 47,329 47,950 Loss from operations (28,610) (28,224) (27,615) (40,542) Non-cash interest expense on liability related to sale of future royalty (5,143) (5,059) (4,972) (4,956) Other income (expense), net 13 56 659 (424) Net loss $ (33,740) $ (33,227) $ (31,928) $ (45,922) Basic and diluted net loss per common share $ $ $ $

Stub Period Comparative Data (U

Stub Period Comparative Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Stub Period Comparative Data (Unaudited)
Stub Period Comparative Data (Unaudited)	M. Stub Period Comparative Data (Unaudited) The unaudited, condensed consolidated statements of earnings for the year ended December 31, 2016 and the six months ended December 31, 2015 is as follows: Year Ended Six Months Ended December 31, December 31, 2016 2015 Revenues: License and milestone fees $ 15,305 $ 16,762 Royalty revenue — 195 Non-cash royalty revenue related to the sale of future royalties 26,218 11,975 Research and development support 5,175 1,620 Clinical materials revenue 1,930 2,328 Total revenues 48,628 32,880 Operating Expenses: Research and development 141,312 73,331 General and administrative 38,528 16,383 Restructuring charge 4,431 — Total operating expenses 184,271 89,714 Loss from operations (135,643) (56,834) Investment income, net 473 111 Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes (18,593) (10,202) Interest expense on convertible senior notes (2,387) — Other expense, net (583) (42) Net loss $ (156,733) $ (66,967) Basic and diluted net loss per common share $ $

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Summary of Significant Accounting Policies
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, ImmunoGen Securities Corp., ImmunoGen Europe Limited, ImmunoGen (Bermuda) Ltd., ImmunoGen BioPharma (Ireland) Limited, and Hurricane, LLC. All intercompany transactions and balances have been eliminated.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States (U.S.) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Subsequent Events	Subsequent Events The Company has evaluated all events or transactions that occurred after December 31, 2018 up through the date the Company issued these financial statements. In January 2019, the Company sold its residual rights to receive royalty payments on commercial sales of Kadcyla to OMERS, the defined benefit pension plan for municipal employees in the Province of Ontario, Canada, for $65.2 million, net of fees. On March 1, 2019, the Company announced that FORWARD I did not meet its PFS primary endpoint in either the entire study population or in the pre-specified subset of patients with high-FRα expression. The Company plans to conduct a full review of the FORWARD I data to determine potential next steps with mirvetuximab as a single agent, and assess its ongoing FORWARD II combination studies as a separate path forward to support a registration in ovarian cancer. The Company did not have any other material recognizable or unrecognizable subsequent events.
Adoption of ASC Topic 606, Revenue from Contracts with Customers	Adoption of ASC Topic 606, Revenue from Contracts with Customers The Company adopted Accounting Standards Codification Topic or ASC, 606 – Revenue from Contracts with Customers , (ASC 606) on January 1, 2018, using the modified retrospective method for all contracts not completed as of the date of adoption. The reported results for 2018 reflect the application of ASC 606 guidance, while the reported results prior to 2018 were prepared under the guidance of ASC 605, Revenue Recognition (ASC 605), which is also referred to herein as "legacy GAAP" or the "previous guidance."
Revenue Recognition	Revenue Recognition The Company enters into licensing and development agreements with collaborators for the development of ADCs. The terms of these agreements contain multiple deliverables/performance obligations which may include (i) licenses, or options to obtain licenses, to the Company’s ADC technology, (ii) rights to future technological improvements, (iii) research activities to be performed on behalf of the collaborative partner, (iv) delivery of cytotoxic agents, and (v) prior to the decommission of the Company’s Norwood facility in 2018, the manufacture of preclinical or clinical materials for the collaborative partner. Payments to the Company under these agreements may include upfront fees, option fees, exercise fees, payments for research activities, payments for the manufacture of preclinical or clinical materials, payments based upon the achievement of certain milestones, and royalties on product sales. Prior to 2018, the Company identified the deliverables included within the agreement and evaluated which deliverables represented separate units of accounting based on whether certain criteria are met, including whether the delivered element had stand‑alone value to the collaborator in accordance with ASC 605. The consideration received was allocated among the separate units of accounting, and the applicable revenue recognition criteria were applied to each of the separate units. In 2018, revenue is recognized when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services in accordance with ASC 606. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under the agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when or as the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when or as the performance obligation is satisfied. As part of the accounting for the arrangement, the Company must develop assumptions that require judgment to determine the selling price for each deliverable under ASC 605 and performance obligation under ASC 606 that were identified in the contract, which is discussed in further detail below. At December 31, 2018, the Company had the following material types of agreements with the parties identified below: · Development and commercialization licenses, which provide the party with the right to use the Company’s ADC technology and/or certain other intellectual property to develop and commercialize anticancer compounds to a specified antigen target: Bayer (one exclusive single-target license) Biotest (one exclusive single-target license) CytomX (one exclusive single-target license) Debiopharm (one exclusive single-compound license) Fusion Pharmaceuticals (one exclusive single-target license) Novartis (five exclusive single-target licenses) Oxford BioTherapeutics/Menarini (one exclusive single target license sublicensed from Amgen) Roche, through its Genentech unit (five exclusive single-target licenses) Sanofi (five fully-paid, exclusive single-target licenses) Takeda, through its wholly owned subsidiary, Millennium Pharmaceuticals, Inc. (one exclusive single-target license) · Collaboration and option agreement for a defined period of time to secure development and commercialization licenses to develop and commercialize specified anticancer compounds on established terms: Jazz Pharmaceuticals · Collaboration and license agreement to co-develop and co-commercialize a specified anticancer compound on established terms: MacroGenics There are no performance, cancellation, termination, or refund provisions in any of the arrangements that contain material financial consequences to the Company. Development and Commercialization Licenses The obligations under a development and commercialization license agreement generally include the license to the Company’s ADC technology with respect to a specified antigen target, and may also include obligations related to rights to future technological improvements, research activities to be performed on behalf of the collaborative partner and the manufacture of preclinical or clinical materials for the collaborative partner. Generally, development and commercialization licenses contain non‑refundable terms for payments and, depending on the terms of the agreement, provide that the Company will (i) at the collaborator’s request, provide research services at negotiated prices which are generally consistent with what other third parties would charge, (ii) prior to the decommissioning of the Company’s Norwood facility in 2018, at the collaborator’s request, manufacture and provide preclinical and clinical materials or deliver cytotoxic agents at negotiated prices which are generally consistent with what other third parties would charge, (iii) earn payments upon the achievement of certain milestones, and (iv) earn royalty payments, generally until the later of the last applicable patent expiration or 10 to 12 years after product launch. Royalty rates may vary over the royalty term depending on the Company’s intellectual property rights and/or the presence of comparable competing products. In the case of Sanofi, its licenses are fully-paid and no further milestones or royalties will be received. In the case of Debiopharm, no royalties will be received. The Company may provide technical assistance and share any technology improvements with its collaborators during the term of the collaboration agreements. The Company does not directly control when or whether any collaborator will request research or, achieve milestones or become liable for royalty payments. In determining the units of accounting under ASC 605, management evaluated whether the license had stand‑alone value from the undelivered elements to the collaborative partner based on the consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research capabilities of the partner and the availability of ADC technology research expertise in the general marketplace. If the Company concluded that the license had stand‑alone value and therefore accounted for as a separate unit of accounting, the Company then determined the estimated selling prices of the license and all other units of accounting. In determining the performance obligations under ASC 606, management evaluates whether the license is distinct, and has significant standalone functionality, from the undelivered elements to the collaborative partner based on the consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research capabilities of the partner and the availability of ADC technology research expertise in the general marketplace and whether technological improvements are required for the continued functionality of the license. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. The Company determined that the estimated selling price under ASC 605 and the stand-alone selling price under ASC 606 to be consistent. The estimates the selling prices of the license and all other deliverables under ASC 605 and performance obligations under ASC 606 are based on market conditions, similar arrangements entered into by third parties, and entity‑specific factors such as the terms of the Company’s previous collaborative agreements, recent preclinical and clinical testing results of therapeutic products that use the Company’s ADC technology, the Company’s pricing practices and pricing objectives, the likelihood that technological improvements will be made, and, if made, will be used by the Company’s collaborators and the nature of the research services to be performed on behalf of its collaborators and market rates for similar services. The Company recognizes revenue related to research services under ASC 605 and ASC 606 as the services are performed. The Company performs research activities, including developing antibody specific conjugation processes, on behalf of its collaborators and potential collaborators during the early evaluation and preclinical testing stages of drug development. The Company also develops conjugation processes for materials for later stage testing and commercialization for certain collaborators. The Company is compensated at negotiated rates that are consistent with what other third parties would charge and may receive milestone payments for developing these processes which are also recorded as a component of research and development support revenue. The Company may also produce research material for potential collaborators under material transfer agreements. The Company records amounts received for research materials produced or services performed as a component of research and development support revenue. The Company may also provide cytotoxic agents to its collaborators and previously produced preclinical and clinical materials (drug substance) at negotiated prices generally consistent with what other third parties would charge. The Company recognizes revenue on cytotoxic agents and, previously, on preclinical and clinical materials when the materials have passed all quality testing required for collaborator acceptance and control has transferred under ASC 606 to the collaborator, while ASC 605 required title and risk of loss to transfer. The majority of the Company’s costs to produce these preclinical and clinical materials were fixed and then allocated to each batch based on the number of batches produced during the period. Therefore, the Company’s costs to produce these materials were significantly affected by the number of batches produced during the period. The volume of preclinical and clinical materials the Company produced was directly related to the scale and scope of preclinical activities and the number of clinical trials the Company and its collaborators were preparing for or currently had underway, the speed of enrollment in those trials, the dosage schedule of each clinical trial and the time period such trials last. Accordingly, the volume of preclinical and clinical materials produced, and therefore the Company’s per‑batch costs to manufacture these preclinical and clinical materials, varied significantly from period to period, which affected the margins recognized on such product sales. The Company recognizes revenue related to the rights to future technological improvements under ASC 605 and ASC 606 over the estimated term of the applicable license. The Company’s development and commercialization license agreements have milestone payments which for reporting purposes are aggregated into three categories: (i) development milestones, (ii) regulatory milestones, and (iii) sales milestones. Development milestones are typically payable when a product candidate initiates or advances into different clinical trial phases. Regulatory milestones are typically payable upon submission for marketing approval with the U.S. Food and Drug Administration, or FDA, or other countries’ regulatory authorities or on receipt of actual marketing approvals for the compound or for additional indications. Sales milestones are typically payable when annual sales reach certain levels. Under ASC 605, at the inception of each agreement that includes milestone payments, the Company evaluated whether each milestone was substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation included an assessment of whether (a) the consideration was commensurate with either (1) the entity’s performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the entity’s performance to achieve the milestone, (b) the consideration related solely to past performance and (c) the consideration was reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone and whether the milestone consideration was reasonable relative to all deliverables and payment terms in the arrangement in making this assessment. Non‑refundable development and regulatory milestones that were expected to be achieved as a result of the Company’s efforts during the period of substantial involvement were considered substantive and were recognized as revenue upon the achievement of the milestone, assuming all other revenue recognition criteria under ASC 605 were met. Milestones that were not considered substantive because the Company did not contribute effort to the achievement of such milestones were generally achieved after the period of substantial involvement and were recognized as revenue upon achievement of the milestone, as there were no undelivered elements remaining and no continuing performance obligations, assuming all other revenue recognition criteria under ASC 605 were met. Under ASC 606, at the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service. If the milestone payment is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method. In addition, the Company evaluates the milestone to determine whether the milestone is considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated; otherwise, such amounts are considered constrained and excluded from the transaction price. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development or regulatory milestones and any related constraint, and if necessary, adjusts its estimate of the transaction price. Any such adjustments to the transaction price are allocated to the performance obligations on the same basis as at contract inception. Amounts allocated to a satisfied performance obligation shall be recognized as revenue, or as a reduction of revenue, in the period in which the transaction price changes. For development and commercialization license agreements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue under ASC 606 at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied) in accordance with the royalty recognition constraint. Under the Company’s development and commercialization license agreements, except for the Sanofi and Debiopharm licenses, the Company receives royalty payments based upon its licensees’ net sales of covered products. Generally, under the development and commercialization agreements, the Company receives royalty reports and payments from its licensees approximately one quarter in arrears. The Company estimates the amount of royalty revenue to be recognized based on historical and forecasted sales and/or sales information from its licensees if available. Under ASC 605, royalty revenue was recognized when it could reliably estimate such amounts and collectability was reasonably assured. As such, the Company generally recognized revenue for sales royalties in the quarter the amounts were reported to the Company by its licensees, or one quarter following the quarter in which sales by the Company’s licensees occurred. Collaboration and Option Agreements/Right-to-Test Agreements The Company’s right-to-test agreements provide collaborators the right to test the Company’s ADC technology for a defined period of time through a research, or right‑to‑test, license. Under both right-to-test agreements and collaboration and option agreements, collaborators may (a) take options, for a defined period of time, to specified targets and (b) upon exercise of those options, secure or “take” licenses to develop and commercialize products for the specified targets on established terms. Under these agreements, fees may be due to the Company (i) at the inception of the arrangement (referred to as “upfront” fees or payments), (ii) upon the opt-in to acquire a development and commercialization license(s) (referred to as exercise fees or payments earned, if any, when the development and commercialization license is “taken”), (iii) at the collaborator’s request, after providing research services at negotiated prices which are generally consistent with what other third parties would charge, or (iv) some combination of all of these fees. The accounting for collaboration and option agreements and right-to-test agreements under ASC 605 and ASC 606 is dependent on the nature of the options granted to the collaborative partner. Under ASC 605, options are considered substantive if, at the inception of the agreement, the Company is at risk as to whether the collaborative partner will choose to exercise the options to secure development and commercialization licenses. Factors that are considered in evaluating whether options are substantive include the overall objective of the arrangement, the benefit the collaborator might obtain from the agreement without exercising the options, the cost to exercise the options relative to the total upfront consideration, and the additional financial commitments or economic penalties imposed on the collaborator as a result of exercising the options. The exercise price for non-substantive options are included in the initial consideration. In determining the units of accounting for substantive options, management evaluates whether the options have stand‑alone value from the undelivered elements to the collaborative partner based on the consideration of the relevant facts and circumstances. If the Company concludes that an option has stand‑alone value and therefore will be accounted for as a separate unit of accounting, it then determines the estimated selling prices of the option and all other units of accounting based on an option pricing model using the following inputs; a) estimated fair value of each program, b) the amount the partner would pay to exercise the option to obtain the license, c) volatility during the expected term of the option and d) risk free interest rate. A risk adjusted discounted cash flow model is then used to estimate the fair value of the option with volatility determined using the stock prices of comparable companies. The cash flow is discounted at a rate representing the Company’s estimate of its cost of capital at the time. Under ASC 606, options are considered distinct performance obligations if they provide a collaborator with a material right. Factors that are considered in evaluating whether options convey a material right include the overall objective of the arrangement, the benefit the collaborator might obtain from the agreement without exercising the options, the cost to exercise the options relative to the fair value of the licenses, and the additional financial commitments or economic penalties imposed on the collaborator as a result of exercising the options. As of December 31, 2018, all right-to-test agreements have expired. If the Company concludes that an option provides the customer a material right, and therefore is a separate performance obligation, the Company then determines the estimated selling prices of the option and all other units of accounting using the following inputs: a) estimated fair value of each program, b) the amount the partner would pay to exercise the option to obtain the license and c) probability of exercise. The Company does not control when or if any collaborator will exercise its options for development and commercialization licenses. As a result, the Company cannot predict when or if it will recognize revenues in connection with any of the foregoing. Upfront payments on development and commercialization licenses may be recognized upon delivery of the license if facts and circumstances dictate that the license has stand-alone functionality and is distinct from the undelivered elements. In determining whether a collaboration and option agreement is within the scope of ASC 808, Collaborative Arrangements , management evaluates the level of involvement of both companies in the development and commercialization of the products to determine if both parties are active participants and if both parties are exposed to risks and rewards dependent on the commercial success of the licensed products. If the agreement is determined to be within the scope of ASC 808, the Company will segregate the research and development activities and the related cost sharing arrangement. Payments made by the Company for such activities will be recorded as research and development expense and reimbursements received from its partner will be recognized as an offset to research and development expense. Transaction Price Allocated to Future Performance Obligations Remaining performance obligations under ASC 606 represent the transaction price of contracts for which work has not been performed (or has been partially performed) and includes unexercised contract options that are considered material rights. As of December 31, 2018, the aggregate amount of the transaction price allocated to remaining performance obligations comprising deferred revenue was $80.8 million. The Company expects to recognize revenue on approximately .4%, 1.6%, and 98% of the remaining performance obligations over the next 12 months, 13 to 60 months, and 61 to 120 months, respectively, however it does not control when or if any collaborator will exercise its options for, or terminate existing development and commercialization licenses. Contract Balances from Contracts with Customers The following table presents changes in the Company’s contract assets and contract liabilities during the year ended December 31, 2018 (in thousands): Balance at Balance at January 1, 2018 End (ASC 606 adoption) Additions Deductions Impact of Netting of Period Contract asset $ — $ 500 $ (5,000) $ 5,000 $ 500 Contract liabilities $ 89,967 $ 730 $ (14,895) $ 5,000 $ 80,802 During the year ended December 31, 2018, the Company recognized the following revenues as a result of changes in contract asset and contract liability balances in the respective periods (in thousands): Year Ended December 31, 2018 Revenue recognized in the period from: Amounts included in contract liabilities at the beginning of the period $ 14,139 Performance obligations satisfied in previous periods $ 1,476 As a result of adoption of ASC 606, a contract asset of $5 million was recorded for a probable milestone which was subsequently earned and paid during the year ended December 31, 2018. During 2018, a milestone from Fusion was deemed probable, and accordingly, a contract asset was created in the amount of $500,000. In December 2018, the Company recorded a $1 million development milestone earned under a sublicense agreement with Oxford BioTherapeutics Ltd. as revenue, which is included in accounts receivable as of December 31, 2018. Also, as a result of Takeda not executing a second license it had available, or extending or expanding its right-to-test agreement, the Company recognized $10.9 million of revenue previously deferred, with a net reduction in deferred revenue of $5.9 million due to contract asset and contract liability netting. In addition, $750,000 of the deferred revenue balance at December 31, 2017 was recognized as revenue during the year ended December 31, 2018 upon completion of the Debiopharm and another collaborator’s performance obligations, $2.1 million of amortization of deferred revenue was recorded related to numerous collaborators’ rights to technological improvements and $335,000 of deferred revenue was recognized upon shipment of clinical materials to a partner and is included in clinical material revenue. The timing of revenue recognition, billings, and cash collections results in billed receivables, contract assets, and contract liabilities on the consolidated balance sheets. When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded. Contract liabilities are recognized as revenue after control of the products or services is transferred to the customer and all revenue recognition criteria have been met.
Financial Instruments and Concentration of Credit Risk	Financial Instruments and Concentration of Credit Risk Cash and cash equivalents are primarily maintained with three financial institutions in the U.S. Deposits with banks may exceed the amount of insurance provided on such deposits. Generally, these deposits may be redeemed upon demand and, therefore, bear minimal risk. The Company’s cash equivalents consist of money market funds with underlying investments primarily being U.S. Government‑issued securities and high quality, short‑term commercial paper. Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents, and marketable securities. The Company held no marketable securities as of December 31, 2018 or 2017. The Company’s investment policy, approved by the Board of Directors, limits the amount it may invest in any one type of investment, thereby reducing credit risk concentrations.
Cash and Cash Equivalents	Cash and Cash Equivalents All highly liquid financial instruments with maturities of three months or less when purchased are considered cash equivalents. As of December 31, 2018 and 2017, the Company held $262.3 million and $267.1 million, respectively, in cash and money market funds consisting principally of U.S. Government-issued securities and high quality, short-term commercial paper which were classified as cash and cash equivalents.
Non-cash Investing and Financing Activities	Non-cash Investing Activities The Company had $715,000 and $482,000 of accrued capital expenditures as of December 31, 2018 and 2017 which have been treated as a non-cash investing activity and, accordingly, are not reflected in the consolidated statement of cash flows.
Fair Value of Financial Instruments	Fair Value of Financial Instruments ASC Topic 820 defines fair value, establishes a framework for measuring fair value in accordance with accounting principles generally accepted in the U.S., and expands disclosures about fair value measurements. Fair value is defined under ASC Topic 820 as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The standard describes a hierarchy to measure fair value which is based on three levels of inputs, of which the first two are considered observable and the last unobservable, as follows: · Level 1—Quoted prices in active markets for identical assets or liabilities. · Level 2—Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. · Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. As of December 31, 2018, the Company held certain assets that are required to be measured at fair value on a recurring basis. The following table represents the fair value hierarchy for the Company’s financial assets measured at fair value on a recurring basis as of December 31, 2018 (in thousands): Fair Value Measurements at December 31, 2018 Using Quoted Prices in Significant Active Markets for Significant Other Unobservable Identical Assets Observable Inputs Inputs Total (Level 1) (Level 2) (Level 3) Cash equivalents $ 242,604 $ 242,604 $ — $ — As of December 31, 2017, the Company held certain assets that are required to be measured at fair value on a recurring basis. The following table represents the fair value hierarchy for the Company’s financial assets measured at fair value on a recurring basis as of December 31, 2017 (in thousands): Fair Value Measurements at December 31, 2017 Using Quoted Prices in Significant Active Markets for Significant Other Unobservable Identical Assets Observable Inputs Inputs Total (Level 1) (Level 2) (Level 3) Cash equivalents $ 240,013 $ 240,013 $ — $ — The fair value of the Company’s cash equivalents is based primarily on quoted prices from active markets. The carrying amounts reflected in the consolidated balance sheets for accounts receivable, unbilled revenue, prepaid and other current assets, accounts payable, accrued compensation, and other accrued liabilities approximate fair value due to their short‑term nature. The gross carrying amount and estimated fair value of the convertible 4.5% senior notes was $2.1 million and $2.8 million, respectively, as of December 31, 2018 compared to $2.1 million and $3.8 million, respectively, as of December 31, 2017. In the second half of 2017, $97.9 million of convertible debt outstanding was converted to 26,160,187 shares of the Company’s common stock causing the decrease in the gross carrying amount. The estimated fair value per $1,000 note on the debt remaining as of December 31, 2018 decreased compared to December 31, 2017 due primarily to a decrease in the Company’s stock price. The fair value of the Convertible Notes is influenced by interest rates, the Company’s stock price and stock price volatility and is determined by prices for the Convertible Notes observed in a market which is a Level 2 input for fair value purposes due to the low frequency of trades.
Inventory	Inventory Inventory costs relate to clinical trial materials being manufactured for sale to the Company’s collaborators. Inventory is stated at the lower of cost or net realizable value as determined on a first‑in, first‑out (FIFO) basis. Inventory at December 31, 2018 and 2017 is summarized below (in thousands): December 31, December 31, 2018 2017 Raw materials $ — $ 40 Work in process — 998 Total $ — $ 1,038 In February 2018, the Company made the decision to implement a new operating model that will rely on external manufacturing and quality testing for drug substance and drug product for its internal development programs, and would discontinue providing such services to its collaborators. The implementation of this new operating model led to the ramp-down and ultimate discontinuation of manufacturing and quality activities at the Company’s Norwood, Massachusetts facility during 2018, and accordingly, there was no inventory on-hand as of December 31, 2018. Raw materials inventory historically consisted entirely of proprietary cell‑killing agents the Company developed as part of its ADC technology. Work in process inventory at December 31, 2017 consisted of drug substance manufactured for sale to the Company’s collaborators to be used in preclinical and clinical studies. All conjugate was made to order at the request of the collaborators and subject to the terms and conditions of respective supply agreements. Based on historical reprocessing or reimbursement required for drug substance that did not meet specification and the status of conjugate on hand or conjugate shipped to collaborators but not yet released per the terms of the respective supply agreements, no reserve for work in process inventory was determined to be required at December 31, 2017. The Company’s costs to manufacture conjugate on behalf of its partners are greater than the supply prices charged to partners, and therefore costs are capitalized into inventory at the supply prices which represent net realizable value. Raw materials inventory cost is stated net of a $1.1 million write-down as of December 31, 2017. The write‑down represents the cost of raw materials that the Company considers to be in excess of a twelve‑month supply based on firm, fixed orders and projections from its collaborators as of the respective balance sheet date. The Company produced preclinical and clinical materials for its collaborators either in anticipation of or in support of preclinical studies and clinical trials, or for process development and analytical purposes. Under the terms of supply agreements with its collaborators, the Company generally received rolling six‑month firm, fixed orders for conjugate that the Company was required to manufacture, and rolling twelve‑month manufacturing projections for the quantity of conjugate the collaborator expected to need in any given twelve‑month period. The amount of clinical material produced was directly related to the number of collaborator anticipated or on‑going clinical trials for which the Company was producing clinical material, the speed of enrollment in those trials, the dosage schedule of each clinical trial and the time period, if any, during which patients in the trial receive clinical benefit from the clinical materials. Because these elements are difficult to estimate over the course of a trial, substantial differences between collaborators’ actual manufacturing orders and their projections could result in the Company’s usage of raw materials varying significantly from estimated usage at an earlier reporting period. To the extent that a collaborator had provided the Company with a firm, fixed order, the collaborator was required by contract to reimburse the Company the full negotiated price of the conjugate, even if the collaborator subsequently canceled the manufacturing run. The Company capitalized raw material as inventory upon receipt and accounted for the raw material inventory as follows: a) to the extent that the Company had up to twelve months of firm, fixed orders and/or projections from its collaborators, the Company capitalized the value of raw materials that will be used in the production of conjugate subject to these firm, fixed orders and/or projections; b) the Company considered more than a twelve month supply of raw materials that was not supported by firm, fixed orders and/or projections from its collaborators to be excess and established a reserve to reduce to zero the value of any such excess raw material inventory with a corresponding charge to research and development expense; and c) the Company also considered any other external factors and information of which it became aware and assessed the impact of such factors or information on the net realizable value of the raw material inventory at each reporting period. During the year ended December 31, 2017, the six month transition period ended December 31, 2016 and fiscal year 2016, the Company obtained additional amounts of its cell-killing agents DMx from its supplier which yielded more material than would be required by the Company’s collaborators over the next twelve months, and as a result, the Company recorded $403,000, $150,000, and $1.1 million, respectively, of charges to research and development expense related to raw material inventory identified as excess. There were no such excess charges during 2018.
Unbilled Revenue	Unbilled Revenue Unbilled revenue substantially represents research funding earned based on actual resources utilized under the Company’s various collaborator agreements.
Clinical Trial Accruals	Clinical Trial Accruals Clinical trial expenses are a significant component of research and development expenses, and the Company outsources a significant portion of these costs to third parties. Third party clinical trial expenses include investigator fees, site costs (patient cost), clinical research organization costs, and costs for central laboratory testing and data management. The accrual for site and patient costs includes inputs such as estimates of patient enrollment, patient cycles incurred, clinical site activations, and other pass-through cost. These inputs are required to be estimated due to a lag in receiving the actual clinical information from third parties. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid asset or accrued clinical trial cost. These third party agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred . Non-refundable advance clinical payments for goods or services that will be used or rendered for future R&D activities recorded as a prepaid asset and recognized as expense as the related goods are delivered or the related services are performed. The Company also records accruals for estimated ongoing clinical research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical clinical accrual estimates made by the Company have not been materially different from the actual costs.
Other Accrued Liabilities	Other Accrued Liabilities Other accrued liabilities consisted of the following at December 31, 2018 and 2017 (in thousands): December 31, December 31, 2018 2017 Accrued contract payments $ 6,389 $ 4,901 Accrued clinical trial costs 11,087 8,400 Accrued professional services 1,171 723 Accrued employee benefits 651 574 Accrued public reporting charges 164 156 Other current accrued liabilities 1,003 1,013 Total $ 20,465 $ 15,767
Deferred Revenue	Deferred Revenue Deferred revenue represents amounts related to partner agreements that have yet to be recognized as revenue. Included in the total of deferred revenue is $5.9 million related to the rights to future technological improvements for our partners at December 31, 2018 and $6.8 million at December 31, 2017. The balance of deferred revenue substantially relates to revenue to be recognized upon the granting of a license to partners.
Research and Development Expenses	Research and Development Expenses The Company’s research and development expenses are charged to expense as incurred and relate to (i) research to evaluate new targets and to develop and evaluate new antibodies, linkers, and cytotoxic agents, (ii) preclinical testing of its own and, in certain instances, its collaborators’ product candidates, and the cost of its own clinical trials, (iii) development related to clinical and commercial manufacturing processes, and (iv) manufacturing operations which also include raw materials. Payments made by the Company in advance for research and development services not yet provided and/or materials not yet delivered and accepted are recorded as prepaid expenses and are included in the accompanying Consolidated Balance Sheets as prepaid and other current assets.
Income Taxes	Income Taxes The Company uses the liability method to account for income taxes. Deferred tax assets and liabilities are determined based on differences between the financial reporting and income tax basis of assets and liabilities, as well as net operating loss carry forwards and tax credits and are measured using the enacted tax rates and laws that will be in effect when the differences reverse. A valuation allowance against net deferred tax assets is recorded if, based on the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.
Property and Equipment	Property and Equipment Property and equipment are stated at cost. The Company provides for depreciation based upon expected useful lives using the straight‑line method over the following estimated useful lives: Machinery and equipment 5 years Computer hardware and software 3 years Furniture and fixtures 5 years Leasehold improvements Shorter of remaining lease term or 7 years Equipment under capital leases is amortized over the lives of the respective leases or the estimated useful lives of the assets, whichever is shorter, and included in depreciation expense. Maintenance and repairs are charged to expense as incurred. Upon retirement or sale, the cost of disposed assets and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the statement of operations. The Company recorded $(115,000), $(239,000), $(1.1 million), and $21,000 of (losses) gains on the sale/disposal of certain furniture and equipment during the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and the year ended June 30, 2016, respectively.
Impairment of Long-Lived Assets	Impairment of Long‑Lived Assets In accordance with ASC Topic 360, “Property, Plant, and Equipment,” the Company continually evaluates whether events or circumstances have occurred that indicate that the estimated remaining useful life of its long‑lived assets may warrant revision or that the carrying value of these assets may be impaired if impairment indicators are present. The Company evaluates the realizability of its long‑lived assets based on cash flow expectations for the related asset. Any write‑downs to fair value are treated as permanent reductions in the carrying amount of the assets. The year ended December 31, 2017 and the six months ended December 31, 2016 include $180,000 and $970,000, respectively, of leasehold impairment charges resulting from the restructuring, the details of which are further discussed in Note I. Based on this evaluation, the Company believes that, as of each of the balance sheet dates presented, none of the Company’s remaining long‑lived assets were impaired.
Computation of Net Loss per Common Share	Computation of Net Loss per Common Share Basic and diluted net loss per share is calculated based upon the weighted average number of common shares outstanding during the period. During periods of income, participating securities are allocated a proportional share of income determined by dividing total weighted average participating securities by the sum of the total weighted average common shares and participating securities (the “two‑class method”). Shares of the Company’s restricted stock participate in any dividends that may be declared by the Company and are therefore considered to be participating securities. Participating securities have the effect of diluting both basic and diluted earnings per share during periods of income. During periods of loss, no loss is allocated to participating securities since they have no contractual obligation to share in the losses of the Company. Diluted (loss) income per share is computed after giving consideration to the dilutive effect of stock options, convertible notes and restricted stock that are outstanding during the period, except where such non-participating securities would be anti-dilutive. The Company’s common stock equivalents, as calculated in accordance with the treasury‑stock method for the options and unvested restricted stock and the if-converted method for the convertible notes, are shown in the following table (in thousands): Six Months Ended Year Ended Years Ended December 31, December 31, June 30, 2018 2017 2016 2016 Options outstanding to purchase common stock, shares issuable under the employee stock purchase plan, and unvested restricted stock at end of period 17,380 14,290 13,878 11,919 Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock 3,001 1,579 1 735 Shares issuable upon conversion of convertible notes at end of period 501 501 23,878 23,878 Common stock equivalents under if-converted method for convertible notes 501 501 23,878 718 The Company’s common stock equivalents have not been included in the net loss per share calculation because their effect is anti‑dilutive due to the Company’s net loss position.
Stock-Based Compensation	Stock‑based Compensation As of December 31, 2018, the Company is authorized to grant future awards under one employee share‑based compensation plan, which is the ImmunoGen, Inc. 2018 Employee, Director and Consultant Equity Incentive Plan, or the 2018 Plan. At the annual meeting of shareholders on June 20, 2018, the 2018 Plan was approved and provides for the issuance of Stock Grants, the grant of Options and the grant of Stock‑Based Awards for up to 7,500,000 shares of the Company’s common stock, as well as up to 19,500,000 shares of common stock which represent awards granted under the previous stock option plans, the ImmunoGen, Inc. 2016 and 2006 Employee, Director and Consultant Equity Incentive Plans, or the 2016 and 2006 Plans, that forfeit, expire, or cancel without delivery of shares of common stock or which resulted in the forfeiture of shares of common stock back to the Company subsequent to June 19, 2018. Option awards are granted with an exercise price equal to the market price of the Company’s stock at the date of grant. Options vest at various periods of up to four years and may be exercised within ten years of the date of grant. The stock‑based awards are accounted for under ASC Topic 718, “Compensation—Stock Compensation.” Pursuant to Topic 718, the estimated grant date fair value of awards is charged to the statement of operations over the requisite service period, which is the vesting period. Such amounts have been reduced by an estimate of forfeitures of all unvested awards. The fair value of each stock option is estimated on the date of grant using the Black‑ Scholes option‑pricing model with the weighted average assumptions noted in the following table. As the Company has not paid dividends since inception, nor does it expect to pay any dividends for the foreseeable future, the expected dividend yield assumption is zero. Expected volatility is based exclusively on historical volatility of the Company’s stock. The expected term of stock options granted is based exclusively on historical data and represents the period of time that stock options granted are expected to be outstanding. The expected term is calculated for and applied to one group of stock options as the Company does not expect substantially different exercise or post‑vesting termination behavior amongst its employee population. The risk‑free rate of the stock options is based on the U.S. Treasury rate in effect at the time of grant for the expected term of the stock options. Six Months Years Ended Ended Year Ended December 31, December 31, June 30, 2018 2017 2016 2016 Dividend None None None None Volatility % % 65.63 % 66.34 % Risk-free interest rate % % 1.29 % 1.80 % Expected life (years) 6.0 6.0 6.3 6.3 Using the Black‑Scholes option‑pricing model, the weighted average grant date fair values of options granted during the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and fiscal year 2016 were $6.70, $1.98, $1.76, and $8.91 per share, respectively. A summary of option activity under the option plans as of December 31, 2018, 2017 and 2016, and changes during the years ended December 31, 2018 and 2017, six-month period ended December 31, 2016, and the fiscal year ended June 30, 2016 is presented below (in thousands, except weighted‑average data): Weighted- Weighted- Number Average Average Aggregate of Stock Exercise Remaining Intrinsic Options Price Life in Yrs. Value Outstanding at June 30, 2015 $ $ — Granted $ Exercised Forfeited/Canceled Outstanding at June 30, 2016 $ — Outstanding at June 30, 2016—vested or unvested and expected to vest $ — Exercisable at June 30, 2016 $ — Outstanding at June 30, 2016 $ Granted Exercised — — Forfeited/Canceled Outstanding at December 31, 2016 10.70 $ 23 Outstanding at December 31, 2016—vested or unvested and expected to vest $ 22 Exercisable at December 31, 2016 $ — Outstanding at December 31, 2016 $ Granted Exercised (191) 3.42 Forfeited/Canceled Outstanding at December 31, 2017 $ 13,513 Outstanding at December 31, 2017—vested or unvested and expected to vest $ $ 13,283 Exercisable at December 31, 2017 $ $ 3,733 Outstanding at December 31, 2017 $ Granted Exercised Forfeited/Canceled 11.49 Outstanding at December 31, 2018 $ $ 5,818 Outstanding at December 31, 2018—vested or unvested and expected to vest $ $ 5,781 Exercisable at December 31, 2018 $ $ 3,122 In September 2018, the Company granted 295,200 performance stock options to certain employees that will vest in two equal installments upon the achievement of specified performance goals within the next five years. These options are included in the table above. None of the awards subject to performance conditions have been expensed to date. The fair value of the performance based options that could be expensed in future periods is $1.8 million. A summary of restricted stock activity under the option plans as of December 31, 2018, 2017, and 2016, and changes during the year ended December 31, 2018 and 2017, and the six-month period ended December 31, 2016, and the fiscal year ended June 30, 2016 is presented below (in thousands, except weighted‑average data): Number of Weighted- Restricted Average Grant Stock Shares Date Fair Value Unvested at June 30, 2015 50 $ Awarded 75 5.65 Vested Unvested at June 30, 2016 $ Awarded 118 Vested — — Forfeited Unvested at December 31, 2016 $ Awarded 2,253 Vested (25) Forfeited (108) Unvested at December 31, 2017 $ Vested (503) Unvested at December 31, 2018 $ In August 2016, February 2017, and June 2017, the Company granted 117,800, 529,830, and 239,000 shares of restricted common stock with grant date fair values of $3.15, $2.47, and $4.71, respectively, to certain officers of the Company, however, 71,380 of these shares have subsequently been forfeited. These restrictions will lapse in three equal installments upon the achievement of specified performance goals within the next five years. None of the awards subject to performance conditions have been expensed to date. The fair value of the performance based shares that could be expensed in future periods is $2.6 million. In June 2018, the Company's Board of Directors, with shareholder approval, adopted the Employee Stock Purchase Plan, or ESPP. An aggregate of 1,000,000 shares of common stock have been reserved for issuance under the ESPP. The ESPP is generally available to all employees who have been continuously employed for three months per year, have customary employment of more than five months in a calendar year, and more than 20 hours per week. Under the ESPP, eligible participants purchase shares of the Company's common stock at a price equal to 85% of the lesser of the closing price of the Company's common stock on the first business day and the final business day of the applicable plan purchase period. Plan purchase periods are six months and begin on January 1 and July 1 of each year, with purchase dates occurring on the final business day of the given purchase period. To pay for the shares, each participant authorizes periodic payroll deductions of up to 15% of his or her eligible cash compensation. All payroll deductions collected from the participant during a purchase period are automatically applied to the purchase of common stock on that period's purchase date provided the participant remains an eligible employee and has not withdrawn from the ESPP prior to that date and are subject to certain limitations imposed by the ESPP and the Internal Revenue Code. On December 31, 2018, 205,000 shares were issued to participating employees at a fair value of approximately $3.55 per share. The fair value of each ESPP award is estimated on the first day of the offering period using the Black-Scholes option-pricing model. The expected volatility used in the fair value calculation was 70.1%, the expected life was .5 years, the expected dividend yield was zero, and the risk-free rate was 2.14%. The Company recognizes share-based compensation expense equal to the fair value of the ESPP awards on a straight-line basis over the offering period. Stock compensation expense related to stock options and restricted stock awards granted under the option plans was $16.4, $11.1, $8.1, and $21.9 million during the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and the fiscal year ended June 30, 2016, respectively. During the years ended December 31, 2018 and 2017, the Company recorded approximately $116,000 and $742,000 of stock compensation cost related to the modification of certain outstanding common stock options with former officers of the Company. During fiscal year 2016, the Company recorded $3.1 million of stock compensation cost related to the modification of certain outstanding common stock options with the former Chief Executive Officer. No similar charges were recorded in the six-month transition period ended December 31, 2016. As of December 31, 2018, the estimated fair value of unvested employee awards was $28.0 million, net of estimated forfeitures. The weighted‑average remaining vesting period for these awards is approximately two years. Included in stock compensation expense for the years ended December 31, 2018 and 2017, the six months ended December 31, 2016, and the fiscal year ended June 30, 2016 are 361,000, 206,000, $215,000, and $380,000, respectively, of expense recorded for directors’ deferred share units, the details of which are discussed in Note H of the Company’s consolidated financial statements. A summary of option activity for options vested during the years ended December 31, 2018 and 2017 and the six months ended December 31, 2016, and the fiscal year ended June 30, 2016 is presented below (in thousands): Years Ended December 31, Six Months Ended December 31, Year Ended June 30, 2018 2017 2016 2016 Total fair value of options vested $ 7,496 $ 10,964 $ 17,121 $ 15,298 Total intrinsic value of options exercised 3,787 598 — 3,142 Cash received for exercise of stock options 4,301 650 — 5,161
Comprehensive Loss	Comprehensive Loss The Company presents comprehensive loss in accordance with ASC Topic 220, Comprehensive Income. Comprehensive loss is comprised of the Company’s net loss for all periods presented.
Segment Information	Segment Information During all periods presented, the Company continued to operate in one reportable business segment under the management approach of ASC Topic 280, Segment Reporting , which is the business of the discovery and development of ADCs for the treatment of cancer. The percentages of revenues recognized from significant customers of the Company in the years ended December 31, 2018, and 2017, the six months ended December 31, 2016, and the year ended June 30, 2016 are included in the following table: Years Ended December 31, Six Months Ended December 31, Year Ended June 30, Collaborative Partner: 2018 2017 2016 2016 Bayer — % — % — % 17 % CytomX 8 % 13 % — % — % Debiopharm 2 % 26 % — % — % Lilly 2 % 1 % 4 % 11 % Novartis 2 % — % 24 % 1 % Roche 60 % 24 % 60 % 43 % Sanofi — % 31 % — % — % Takeda 23 % 4 % 8 % 16 % There were no other customers of the Company with significant revenues in the periods presented.
Other Recently Adopted Accounting Pronouncements and Recently issued ASUs, not yet adopted	Other Recently Adopted Accounting Pronouncements In January 2016, the FASB issued ASU 2016-1, Recognition and Measurement of Financial Assets and Financial Liabilities (Topic 825). The amendments in this ASU supersede the guidance to classify equity securities with readily determinable fair values into different categories (that is, trading or available-for-sale) and require equity securities (including other ownership interests, such as partnerships, unincorporated joint ventures, and limited liability companies) to be measured at fair value with changes in the fair value recognized through net income. The amendments allow equity investments that do not have readily determinable fair values to be remeasured at fair value either upon the occurrence of an observable price change or upon identification of an impairment. The amendments also require enhanced disclosures about those investments. The amendments improve financial reporting by providing relevant information about an entity’s equity investments and reducing the number of items that are recognized in other comprehensive income. This guidance is effective for annual reporting beginning after December 15, 2017, including interim periods within the year of adoption, and calls for prospective application, with early application permitted. Accordingly, the standard is effective for the Company on January 1, 2018. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, Stock Compensation – Scope of Modification Accounting (Topic 718) regarding changes to terms and conditions of share-based payment awards. The ASU provides guidance about which changes to terms or conditions of a share-based payment award require an entity to apply modification accounting. The guidance is effective for annual periods beginning after December 15, 2017, including interim periods within that year. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements. Recently issued accounting pronouncements, not yet adopted In February 2016, the FASB issued ASU 2016-2, Leases (Topic 842) . The purpose of this update is to increase the transparency and comparability among organizations by recognizing lease assets and liabilities on the balance sheet, including those previously classified as operating leases under current U.S. GAAP, and disclosing key information about leasing arrangements. Topic 842 as amended is effective for annual periods beginning after December 15, 2018, including interim periods within those annual periods. The Company currently plans to adopt the standard using the transition method provided by ASC Update No. 2018-11, Leases (Topic 842): Targeted Improvements . Under this method, the Company will initially apply the new leasing rules on January 1, 2019, rather than at the earliest comparative period presented in the financial statements. Prior periods presented will be in accordance with the existing lease guidance. Upon transition, the Company plans to apply the package of practical expedients permitted under Topic 842 transition guidance to its entire lease portfolio at January 1, 2019. As a result, the Company is not required to reassess (i) whether any expired or existing contracts are or contain leases, (ii) the classification of any expired or existing leases, and (iii) initial direct costs for any existing leases. Furthermore, the Company will be electing not to separate lease and non-lease components for our leases. Instead, for these applicable classes of underlying assets, the Company will account for each separate lease component and the non-lease components associated with that lease component, as a single lease component. Lastly, the Company will be electing not to apply the recognition requirements of ASC 842 to short-term leases and instead to recognize the lease payments as lease cost on a straight-line basis over the lease term. Although the Company has not finalized its process of evaluating the impact of adoption of the ASU on its consolidated financial statements, the Company expects to record an increase in the recorded amounts of assets and liabilities related to the recognition of new right-of-use assets and lease liabilities on the Company’s balance sheet for leases currently classified as operating leases for an amount that is expected to range between $16 million to $19 million. The Company does not expect the adoption to have an impact to the statement of operations. In June 2018, the FASB issued ASU No. 2018-07, Compensation — Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting , which expands the scope of Topic 718 to include all share-based payment transactions for acquiring goods and services from non-employees. ASU 2018-07 specifies that Topic 718 applies to all share-based payment transactions in which the grantor acquires goods and services to be used or consumed in its own operations by issuing share-based payment awards. ASU 2018-07 also clarifies that Topic 718 does not apply to share-based payments used to effectively provide (1) financing to the issuer or (2) awards granted in conjunction with selling goods or services to customers as part of a contract accounted for under ASC 606. ASU 2018-07 is effective for annual periods beginning after December 15, 2018, with early adoption permitted. This ASU is not expected to have a material effect on the Company’s consolidated financial statements. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 , which clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer. In addition, ASU 2018-18 adds unit-of-account guidance to ASC Topic 808, Collaborative Arrangements , in order to align this guidance with ASC 606 and also precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. This guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption is permitted. The Company is currently evaluating the potential impact that ASU 2018-18 may have on the consolidated financial statements. No other recently issued or effective ASUs had, or are expected to have, a material effect on the Company's results of operations, financial condition, or liquidity.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policy Schedules
Contract assets and contract liabilities	The following table presents changes in the Company’s contract assets and contract liabilities during the year ended December 31, 2018 (in thousands): Balance at Balance at January 1, 2018 End (ASC 606 adoption) Additions Deductions Impact of Netting of Period Contract asset $ — $ 500 $ (5,000) $ 5,000 $ 500 Contract liabilities $ 89,967 $ 730 $ (14,895) $ 5,000 $ 80,802 During the year ended December 31, 2018, the Company recognized the following revenues as a result of changes in contract asset and contract liability balances in the respective periods (in thousands): Year Ended December 31, 2018 Revenue recognized in the period from: Amounts included in contract liabilities at the beginning of the period $ 14,139 Performance obligations satisfied in previous periods $ 1,476
Schedule of assets that are required to be measured at fair value on a recurring basis	As of December 31, 2018, the Company held certain assets that are required to be measured at fair value on a recurring basis. The following table represents the fair value hierarchy for the Company’s financial assets measured at fair value on a recurring basis as of December 31, 2018 (in thousands): Fair Value Measurements at December 31, 2018 Using Quoted Prices in Significant Active Markets for Significant Other Unobservable Identical Assets Observable Inputs Inputs Total (Level 1) (Level 2) (Level 3) Cash equivalents $ 242,604 $ 242,604 $ — $ — As of December 31, 2017, the Company held certain assets that are required to be measured at fair value on a recurring basis. The following table represents the fair value hierarchy for the Company’s financial assets measured at fair value on a recurring basis as of December 31, 2017 (in thousands): Fair Value Measurements at December 31, 2017 Using Quoted Prices in Significant Active Markets for Significant Other Unobservable Identical Assets Observable Inputs Inputs Total (Level 1) (Level 2) (Level 3) Cash equivalents $ 240,013 $ 240,013 $ — $ —
Schedule of inventory	Inventory at December 31, 2018 and 2017 is summarized below (in thousands): December 31, December 31, 2018 2017 Raw materials $ — $ 40 Work in process — 998 Total $ — $ 1,038
Schedule of components of other accrued liabilities	Other accrued liabilities consisted of the following at December 31, 2018 and 2017 (in thousands): December 31, December 31, 2018 2017 Accrued contract payments $ 6,389 $ 4,901 Accrued clinical trial costs 11,087 8,400 Accrued professional services 1,171 723 Accrued employee benefits 651 574 Accrued public reporting charges 164 156 Other current accrued liabilities 1,003 1,013 Total $ 20,465 $ 15,767
Schedule of estimated useful lives of property and equipment	Machinery and equipment 5 years Computer hardware and software 3 years Furniture and fixtures 5 years Leasehold improvements Shorter of remaining lease term or 7 years
Schedule of common stock equivalents, as calculated in accordance with the treasury-stock method	The Company’s common stock equivalents, as calculated in accordance with the treasury‑stock method for the options and unvested restricted stock and the if-converted method for the convertible notes, are shown in the following table (in thousands): Six Months Ended Year Ended Years Ended December 31, December 31, June 30, 2018 2017 2016 2016 Options outstanding to purchase common stock, shares issuable under the employee stock purchase plan, and unvested restricted stock at end of period 17,380 14,290 13,878 11,919 Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock 3,001 1,579 1 735 Shares issuable upon conversion of convertible notes at end of period 501 501 23,878 23,878 Common stock equivalents under if-converted method for convertible notes 501 501 23,878 718
Schedule of risk-free rate of the stock options based on US Treasury rate	Six Months Years Ended Ended Year Ended December 31, December 31, June 30, 2018 2017 2016 2016 Dividend None None None None Volatility % % 65.63 % 66.34 % Risk-free interest rate % % 1.29 % 1.80 % Expected life (years) 6.0 6.0 6.3 6.3
Summary of stock option activity	A summary of option activity under the option plans as of December 31, 2018, 2017 and 2016, and changes during the years ended December 31, 2018 and 2017, six-month period ended December 31, 2016, and the fiscal year ended June 30, 2016 is presented below (in thousands, except weighted‑average data): Weighted- Weighted- Number Average Average Aggregate of Stock Exercise Remaining Intrinsic Options Price Life in Yrs. Value Outstanding at June 30, 2015 $ $ — Granted $ Exercised Forfeited/Canceled Outstanding at June 30, 2016 $ — Outstanding at June 30, 2016—vested or unvested and expected to vest $ — Exercisable at June 30, 2016 $ — Outstanding at June 30, 2016 $ Granted Exercised — — Forfeited/Canceled Outstanding at December 31, 2016 10.70 $ 23 Outstanding at December 31, 2016—vested or unvested and expected to vest $ 22 Exercisable at December 31, 2016 $ — Outstanding at December 31, 2016 $ Granted Exercised (191) 3.42 Forfeited/Canceled Outstanding at December 31, 2017 $ 13,513 Outstanding at December 31, 2017—vested or unvested and expected to vest $ $ 13,283 Exercisable at December 31, 2017 $ $ 3,733 Outstanding at December 31, 2017 $ Granted Exercised Forfeited/Canceled 11.49 Outstanding at December 31, 2018 $ $ 5,818 Outstanding at December 31, 2018—vested or unvested and expected to vest $ $ 5,781 Exercisable at December 31, 2018 $ $ 3,122
Summary of restricted stock activity	A summary of restricted stock activity under the option plans as of December 31, 2018, 2017, and 2016, and changes during the year ended December 31, 2018 and 2017, and the six-month period ended December 31, 2016, and the fiscal year ended June 30, 2016 is presented below (in thousands, except weighted‑average data): Number of Weighted- Restricted Average Grant Stock Shares Date Fair Value Unvested at June 30, 2015 50 $ Awarded 75 5.65 Vested Unvested at June 30, 2016 $ Awarded 118 Vested — — Forfeited Unvested at December 31, 2016 $ Awarded 2,253 Vested (25) Forfeited (108) Unvested at December 31, 2017 $ Vested (503) Unvested at December 31, 2018 $
Summary of vested stock option activity	A summary of option activity for options vested during the years ended December 31, 2018 and 2017 and the six months ended December 31, 2016, and the fiscal year ended June 30, 2016 is presented below (in thousands): Years Ended December 31, Six Months Ended December 31, Year Ended June 30, 2018 2017 2016 2016 Total fair value of options vested $ 7,496 $ 10,964 $ 17,121 $ 15,298 Total intrinsic value of options exercised 3,787 598 — 3,142 Cash received for exercise of stock options 4,301 650 — 5,161
Schedule of percentage of total revenues recognized from each significant customer	Years Ended December 31, Six Months Ended December 31, Year Ended June 30, Collaborative Partner: 2018 2017 2016 2016 Bayer — % — % — % 17 % CytomX 8 % 13 % — % — % Debiopharm 2 % 26 % — % — % Lilly 2 % 1 % 4 % 11 % Novartis 2 % — % 24 % 1 % Roche 60 % 24 % 60 % 43 % Sanofi — % 31 % — % — % Takeda 23 % 4 % 8 % 16 %
ASU 2014-09
Accounting Policy Schedules
Schedule of financial statement impact of adopting ASC 606	IMMUNOGEN, INC. ADJUSTED CONSOLIDATED BALANCE SHEET In thousands, except per share amounts Adjustments Balance at December 31, Due to January 1, 2017 ASC 606 2018 ASSETS Cash and cash equivalents $ 267,107 $ — $ 267,107 Accounts receivable 2,649 — 2,649 Unbilled revenue 2,580 — 2,580 Non-cash royalty receivable — 8,900 8,900 Inventory 1,038 — 1,038 Prepaid and other current assets 2,967 — 2,967 Total current assets 276,341 8,900 285,241 Property and equipment, net of accumulated depreciation 14,538 — 14,538 Other assets 3,797 — 3,797 Total assets $ 294,676 $ 8,900 $ 303,576 LIABILITIES AND SHAREHOLDERS’ DEFICIT Accounts payable $ 8,562 $ — $ 8,562 Accrued compensation 11,473 — 11,473 Other accrued liabilities 15,767 — 15,767 Current portion of deferred lease incentive 784 — 784 Current portion of liability related to the sale of future royalties, net 17,779 — 17,779 Current portion of deferred revenue 1,405 41 1,446 Total current liabilities 55,770 41 55,811 Deferred lease incentive, net of current portion 5,129 — 5,129 Deferred revenue, net of current portion 93,752 (5,231) 88,521 Convertible 4.5% senior notes, net 2,050 — 2,050 Liability related to the sale of future royalties, net 151,634 — 151,634 Other long-term liabilities 4,236 — 4,236 Total liabilities 312,571 (5,190) 307,381 Shareholders’ deficit: Preferred stock — — — Common stock 1,325 — 1,325 Additional paid-in capital 1,009,362 — 1,009,362 Accumulated deficit (1,028,582) 14,090 (1,014,492) Total shareholders’ deficit (17,895) 14,090 (3,805) Total liabilities and shareholders’ deficit $ 294,676 $ 8,900 $ 303,576 Under the previous guidance, the Company deferred revenue pertaining to the transfer of certain exclusive commercialization and development licenses, and to account for these agreements under the legacy GAAP, the Company identified the deliverables included within the agreements and evaluated which deliverables represented separate units of accounting based on whether certain criteria were met, including whether the delivered element had stand-alone value to the collaborator. The consideration received was allocated among the separate units of accounting, and the applicable revenue recognition criteria were applied to each of the separate units. Under ASC 606, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is distinct from other performance obligations, is transferred to the customer and the customer is able to use and benefit from the license. Under the previous guidance, milestones that were considered substantive because the Company contributed significant effort to the achievement of such milestones were recognized as revenue upon achievement of the milestone. Under ASC 606, if the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service, the associated milestone value is allocated to that distinct good or service. If a milestone is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method. Under ASC 606, the Company also evaluates the milestone to determine whether the milestone is probable of being achieved and estimates the amount to be included in the transaction price. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated, otherwise, such amounts are constrained and excluded from the transaction price until the probable threshold is met. The Company determined it was probable that a future $5.0 million milestone for Takeda enrolling a patient in a Phase I trial as of the date of adoption would occur and, accordingly, recorded a reduction to accumulated deficit of $4.6 million related to this previously delivered license as approximately $400,000 was allocated to undelivered rights to future technological improvements. The $5.0 million contract asset recorded for the probable milestone was netted against contract liabilities related to the specific contract. Prior to the adoption of ASC 606, the Company recognized royalty revenue when it could reliably estimate such amounts and collectability was reasonably assured. As such, the Company generally recognized revenue for sales royalties in the quarter the amounts were reported to the Company by its licensees, or one quarter following the quarter in which sales by the Company’s licensees occurred. Under ASC 606, if the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). As a result of recognizing royalties for sales in the fourth quarter of fiscal year 2017, the Company recognized a reduction to accumulated deficit of $8.9 million. The net impact of these changes resulted in a $14.1 million reduction to accumulated deficit, a $5.2 million reduction to deferred revenue and an $8.9 million increase in non-cash royalty receivable. The adoption of ASC 606 resulted in the acceleration of revenue through December 31, 2017, which in turn reduced the related net deferred tax asset by $3.9 million. As the Company fully reserves its net deferred tax assets, the impact was offset by the valuation allowance. Impact of ASC 606 Revenue Guidance on Financial Statement Line Items The following tables compare the reported condensed consolidated balance sheet and statement of operations, as of and for the year ended December 31, 2018, to the pro-forma amounts had the previous guidance been in effect: IMMUNOGEN, INC. PRO FORMA CONSOLIDATED BALANCE SHEET In thousands, except per share amounts As of December 31, 2018 Pro forma as if the previous accounting As reported was in effect ASSETS Cash and cash equivalents $ 262,252 $ 262,252 Accounts receivable 1,701 1,701 Unbilled revenue 617 617 Contract asset 500 — Non-cash royalty receivable 9,249 — Inventory — — Prepaid and other current assets 4,462 4,462 Total current assets 278,781 269,032 Property and equipment, net of accumulated depreciation 12,891 12,891 Other assets 3,709 3,709 Total assets $ 295,381 $ 285,632 LIABILITIES AND SHAREHOLDERS’ EQUITY (DEFICIT) Accounts payable $ 11,365 $ 11,365 Accrued compensation 11,796 11,796 Other accrued liabilities 20,465 20,465 Current portion of deferred lease incentive 837 837 Current portion of liability related to the sale of future royalties, net 25,880 25,880 Current portion of deferred revenue 317 297 Total current liabilities 70,660 70,640 Deferred lease incentive, net of current portion 4,675 4,675 Deferred revenue, net of current portion 80,485 83,710 Convertible 4.5% senior notes, net 2,064 2,064 Liability related to the sale of future royalties, net 122,345 122,345 Other long-term liabilities 4,180 4,180 Total liabilities 284,409 287,614 Shareholders’ equity (deficit): Preferred stock — — Common stock 1,494 1,494 Additional paid-in capital 1,192,813 1,192,813 Accumulated deficit (1,183,335) (1,196,289) Total shareholders’ equity (deficit) 10,972 (1,982) Total liabilities and shareholders’ equity (deficit) $ 295,381 $ 285,632 As a result of adoption of ASC 606, a receivable is recorded for royalties earned during the current quarter rather than one quarter in arrears under the previous guidance. Deferred revenue increased under ASC 606 due to a greater amount of the transaction prices being allocated to the future technological improvement rights under ASC 606. IMMUNOGEN, INC. PRO FORMA CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS In thousands, except per share amounts Year ended December 31, 2018 Pro forma as if the previous accounting As reported was in effect Revenues: License and milestone fees $ 15,280 $ 16,765 Non-cash royalty revenue related to the sale of future royalties 32,154 31,805 Research and development support 1,377 1,377 Clinical materials revenue 4,635 4,635 Total revenues 53,446 54,582 Operating Expenses: Research and development 174,456 174,456 General and administrative 36,746 36,746 Restructuring charge 3,693 3,693 Total operating expenses 214,895 214,895 Loss from operations (161,449) (160,313) Investment income, net 4,227 4,227 Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes (10,631) (10,631) Interest expense on convertible senior notes (95) (95) Other (expense) income, net (895) (895) Net loss $ (168,843) $ (167,707) Basic and diluted net loss per common share $ $

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property and Equipment
Schedule of components of property and equipment	Property and equipment consisted of the following at December 31, 2018 and 2017 (in thousands): December 31, December 31, 2018 2017 Leasehold improvements $ 20,684 $ 36,460 Machinery and equipment 22,558 23,123 Computer hardware and software 5,494 8,273 Furniture and fixtures 3,546 3,710 Assets under construction 113 416 $ 52,395 $ 71,982 Less accumulated depreciation (39,504) (57,444) Property and equipment, net $ 12,891 $ 14,538

Liability Related to Sale of _2

Liability Related to Sale of Future Royalties (Tables)	12 Months Ended
	Dec. 31, 2018
Liability Related to Sale of Future Royalties
Schedule of Liability account during the period from the inception of the royalty transaction	The following table shows the activity within the liability account during the year ended December 31, 2018 and the period from inception (in thousands): Twelve Months Period from Ended inception to December 31, December 31, 2018 2018 Liability related to sale of future royalties, net — beginning balance $ 169,413 $ — Proceeds from sale of future royalties, net — 194,135 Kadcyla royalty payments received and paid (31,805) (103,624) Non-cash interest expense recognized 10,617 57,714 Liability related to sale of future royalties, net — ending balance $ 148,225 $ 148,225

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Taxes
Reconciliation of the Company's expected tax benefit, as computed by applying the U.S. federal corporate tax rate to loss before the benefit for income taxes, and actual tax	The difference between the Company’s expected tax benefit, as computed by applying the applicable U.S. federal corporate tax rate to loss before the benefit for income taxes, and actual tax is reconciled in the following chart (in thousands): Six Months Ended Year Ended Years Ended December 31, December 31, June 30, 2018 2017 2016 2016 Loss before income tax expense $ (168,843) $ (96,012) $ (78,883) $ (144,817) Expected tax benefit at 21%, 34%, 34% and 34%, respectively $ (35,457) $ (32,644) $ (26,820) $ (49,238) Permanent differences (103) 25 15 345 Incentive stock options 1,144 1,528 1,313 2,501 State tax benefit net of federal benefit (10,622) (3,537) (4,157) (7,954) Change in valuation allowance, net 53,706 (63,238) 32,922 62,505 Federal research credit (2,466) (2,204) (1,232) (4,109) Federal orphan drug credit (6,934) (7,118) (2,901) (4,241) Expired loss and credit carryforwards — — — 184 Change in U.S. tax law — 97,479 — — Debt inducement — 8,044 — — Lease incentive 109 — — — Stock option expirations 623 1,665 860 7 Benefit for income taxes $ — $ — $ — $ —
Schedule of significant components of deferred tax assets	Significant components of the Company’s deferred tax assets and liabilities as of December 31, 2018 and 2017 are as follows (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 171,437 $ 118,672 Research and development tax credit carryforwards 69,710 58,606 Property and other intangible assets 297 2,272 Deferred revenue 22,075 25,997 Stock-based compensation 12,849 12,125 Deferred lease incentive 2,639 2,889 Other liabilities 2,920 3,037 Royalty sale 38,593 47,143 Total deferred tax assets $ 320,520 $ 270,741 Deferred tax liabilities: Stock-based compensation (156) — Royalty sale transaction costs (625) (859) Total deferred tax liabilities $ (781) $ (859) Valuation allowance (319,739) (269,882) Net deferred tax assets/(liabilities) $ — $ —

Capital Stock (Tables)

Capital Stock (Tables)	12 Months Ended
	Dec. 31, 2018
Capital Stock
Schedule of options exercisable and their respective weighted average exercise prices per share	Weighted‑ Exercisable Average (in thousands) Exercise Price December 31, 2018 8,405 $ 11.47 December 31, 2017 7,996 $ 12.16 December 31, 2016 7,898 $ 13.15 June 30, 2016 6,453 $ 12.63

Restructuring Charge (Tables)

Restructuring Charge (Tables)	12 Months Ended
	Dec. 31, 2018
Restructuring Charge
Schedule activity against the restructuring charge	Employee Termination Benefits Costs Initial charge related to employee benefits - March 2018 $ 1,189 Additional charges during the year 2,347 Payments during the period (2,695) Balance December 31, 2018 $ 841

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies
Schedule of minimum rental commitments	As of December 31, 2018, the minimum rental commitments for the next five years and thereafter under the non‑cancelable operating lease agreements discussed above are as follows (in thousands): 2019 $ 5,498 2020 5,419 2021 5,257 2022 5,323 2023 5,450 Thereafter 12,336 Total minimum lease payments $ 39,283

Quarterly Financial Informati_2

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information (Unaudited)
Schedule of Quarterly Financial Information (Unaudited)	Calendar Year 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, 2018 June 30, 2018 September 30, 2018 December 31, 2018 (In thousands, except per share data) Revenues: License and milestone fees $ 11,540 $ 1,321 $ 672 $ 1,747 Non-cash royalty revenue related to the sale of future royalties 7,190 7,242 8,441 9,281 Research and development support 383 388 388 218 Clinical materials revenue 702 336 1,427 2,170 Total revenues 19,815 9,287 10,928 13,416 Expenses: Research and development 44,831 38,701 47,243 43,681 General and administrative 9,995 8,652 8,347 9,752 Restructuring charge 1,731 686 870 406 Total expenses 56,557 48,039 56,460 53,839 Loss from operations (36,742) (38,752) (45,532) (40,423) Non-cash interest expense on liability related to sale of future royalty (3,046) (2,611) (2,546) (2,428) Interest expense on senior convertible notes (24) (23) (23) (25) Other (expense) income, net 1,199 (238) 1,294 1,077 Net loss $ (38,613) $ (41,624) $ (46,807) $ (41,799) Basic and diluted net loss per common share $ (0.30) $ (0.31) $ (0.32) $ (0.28) Calendar Year 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 (In thousands, except per share data) Revenues: License and milestone fees $ 18,730 $ 31,080 $ 79 $ 29,580 Royalty revenue — — — — Non-cash royalty revenue related to the sale of future royalties 7,613 6,439 6,503 7,587 Research and development support 1,478 902 650 452 Clinical materials revenue 678 599 1,248 1,829 Total revenues 28,499 39,020 8,480 39,448 Expenses: Research and development 32,888 35,319 31,689 39,843 General and administrative 8,119 8,836 7,908 9,048 Restructuring charge 386 — — 393 Total expenses 41,393 44,155 39,597 49,284 Loss from operations (12,894) (5,135) (31,117) (9,836) Non-cash interest expense on liability related to sale of future royalty and convertible senior notes (3,575) (3,501) (3,385) (3,221) Interest expense on senior convertible notes (1,125) (1,125) (762) (28) Non-cash debt conversion expense — — (22,191) (724) Other income, net 249 894 773 691 Net loss $ (17,345) $ (8,867) $ (56,682) $ (13,118) Basic and diluted net loss per common share $ $ $ $ Six Month Transition Period First Quarter Second Quarter Ended Ended September 30, 2016 December 31, 2016 (In thousands, except per share data) Revenues: License and milestone fees $ 76 $ 5,076 Royalty revenue — — Non-cash royalty revenue related to the sale of future royalties 6,184 6,710 Research and development support 1,354 1,427 Clinical materials revenue 46 633 Total revenues 7,660 13,846 Expenses: Research and development 32,909 33,657 General and administrative 9,459 8,536 Restructuring charge 4,130 301 Total expenses 46,498 42,494 Loss from operations (38,838) (28,648) Non-cash interest expense on liability related to sale of future royalty and convertible senior notes (5,018) (3,647) Interest expense on senior convertible notes (1,150) (1,099) Other income (expense), net 275 (758) Net loss $ (44,731) $ (34,152) Basic and diluted net loss per common share $ $ Fiscal Year 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended September 30, 2015 December 31, 2015 March 31, 2016 June 30, 2016 (In thousands, except per share data) Revenues: License and milestone fees $ 6,070 $ 10,692 $ 10,077 $ 76 Royalty revenue — 195 — — Non-cash royalty revenue related to the sale of future royalties 5,684 6,291 7,380 5,944 Research and development support 772 848 1,059 1,335 Clinical materials revenue 2,325 3 1,198 53 Total revenues 14,851 18,029 19,714 7,408 Expenses: Research and development 35,132 38,199 36,094 38,652 General and administrative 8,329 8,054 11,235 9,298 Total expenses 43,461 46,253 47,329 47,950 Loss from operations (28,610) (28,224) (27,615) (40,542) Non-cash interest expense on liability related to sale of future royalty (5,143) (5,059) (4,972) (4,956) Other income (expense), net 13 56 659 (424) Net loss $ (33,740) $ (33,227) $ (31,928) $ (45,922) Basic and diluted net loss per common share $ $ $ $

Stub Period Comparative Data _2

Stub Period Comparative Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Stub Period Comparative Data (Unaudited)
Unaudited condensed consolidated statements of earnings	Year Ended Six Months Ended December 31, December 31, 2016 2015 Revenues: License and milestone fees $ 15,305 $ 16,762 Royalty revenue — 195 Non-cash royalty revenue related to the sale of future royalties 26,218 11,975 Research and development support 5,175 1,620 Clinical materials revenue 1,930 2,328 Total revenues 48,628 32,880 Operating Expenses: Research and development 141,312 73,331 General and administrative 38,528 16,383 Restructuring charge 4,431 — Total operating expenses 184,271 89,714 Loss from operations (135,643) (56,834) Investment income, net 473 111 Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes (18,593) (10,202) Interest expense on convertible senior notes (2,387) — Other expense, net (583) (42) Net loss $ (156,733) $ (66,967) Basic and diluted net loss per common share $ $

Nature of Business and Plan o_2

Nature of Business and Plan of Operations (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended														6 Months Ended		12 Months Ended
	Jan. 31, 2019	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	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Jan. 02, 2018	Jun. 30, 2015
Net loss																$ (78,883)		$ (168,843)	$ (96,012)		$ (144,817)
Accumulated deficit		$ (1,183,335)				$ (1,028,582)												(1,183,335)	(1,028,582)			$ (1,014,492)
Total revenues		13,416	$ 10,928	$ 9,287	$ 19,815	39,448	$ 8,480	$ 39,020	$ 28,499	$ 13,846	$ 7,660	$ 7,408	$ 19,714	$ 18,029	$ 14,851	21,506	$ 32,880	53,446	115,447	$ 48,628	60,002
Cash and cash equivalents		$ 262,252				$ 267,107				$ 159,964		$ 245,026				159,964		$ 262,252	267,107	$ 159,964	245,026	$ 267,107	$ 278,109
Number of months Capital resources meets capital expenditures																		12 months
Non Cash Royalty Revenue Related To Sale of Future Royalties																$ 12,894		$ 32,154	$ 28,142		$ 25,299
Product
Total revenues																		$ 0
OMERS | Subsequent event | Kadcyla
Non Cash Royalty Revenue Related To Sale of Future Royalties	$ 65,200

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Subsequent Event (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended	12 Months Ended
	Jan. 31, 2019	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Subsequent Event [Line Items]
Non Cash Royalty Revenue Related To Sale of Future Royalties		$ 12,894	$ 32,154	$ 28,142	$ 25,299
Kadcyla | Subsequent event | OMERS
Subsequent Event [Line Items]
Non Cash Royalty Revenue Related To Sale of Future Royalties	$ 65,200

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Impact of Adopting ASC 606, Adjusted Balance Sheet (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	May 31, 2018	Jan. 02, 2018	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015
ASSETS
Cash and cash equivalents	$ 262,252,000	$ 267,107,000		$ 267,107,000	$ 159,964,000	$ 245,026,000		$ 278,109,000
Accounts receivable	1,701,000	2,649,000		2,649,000
Unbilled revenue	617,000	2,580,000		2,580,000
Non-cash royalty receivable	9,249,000			8,900,000
Inventory	0	1,038,000		1,038,000
Prepaid and other current assets	4,462,000	2,967,000		2,967,000
Total current assets	278,781,000	276,341,000		285,241,000
Property and equipment, net of accumulated depreciation	12,891,000	14,538,000		14,538,000
Other assets	3,709,000	3,797,000		3,797,000
Total assets	295,381,000	294,676,000		303,576,000
LIABILITIES AND SHAREHOLDERS' EQUITY (DEFICIT)
Accounts payable	11,365,000	8,562,000		8,562,000
Accrued compensation	11,796,000	11,473,000		11,473,000
Other accrued liabilities	20,465,000	15,767,000		15,767,000
Current portion of deferred lease incentive	837,000	784,000		784,000
Current portion of liability related to the sale of future royalties, net	25,880,000	17,779,000		17,779,000
Current portion of deferred revenue	317,000	1,405,000		1,446,000
Total current liabilities	70,660,000	55,770,000		55,811,000
Deferred lease incentive, net of current portion	4,675,000	5,129,000		5,129,000			$ 2,000,000
Deferred revenue, net of current portion	80,485,000	93,752,000		88,521,000
Convertible 4.5% senior notes, net	2,064,000	2,050,000		2,050,000
Liability related to the sale of future royalties, net	122,345,000	151,634,000		151,634,000
Other long-term liabilities	4,180,000	4,236,000		4,236,000
Total liabilities	284,409,000	312,571,000		307,381,000
Shareholders' deficit:
Preferred stock
Common stock	1,494,000	1,325,000		1,325,000
Additional paid-in capital	1,192,813,000	1,009,362,000		1,009,362,000
Accumulated deficit	(1,183,335,000)	(1,028,582,000)		(1,014,492,000)
Total shareholders' equity (deficit)	10,972,000	(17,895,000)		(3,805,000)	$ (152,850,000)	$ (82,304,000)		$ 35,104,000
Total liabilities and shareholders' equity (deficit)	295,381,000	294,676,000		303,576,000
Reduction to accumulated deficit related to previously delivered license	1,476,000
Deferred tax assets:
Increase (decrease) in valuation allowance	49,900,000
Milestone recognized as contract asset	500,000
Takeda
Shareholders' deficit:
Accumulated deficit				4,600,000
Deferred tax assets:
Potential milestone payment									$ 210,000,000
Pro forma as if previous accounting was in effect | ASU 2014-09
ASSETS
Cash and cash equivalents	262,252,000	267,107,000
Accounts receivable	1,701,000	2,649,000
Unbilled revenue	617,000	2,580,000
Inventory		1,038,000
Prepaid and other current assets	4,462,000	2,967,000
Total current assets	269,032,000	276,341,000
Property and equipment, net of accumulated depreciation	12,891,000	14,538,000
Other assets	3,709,000	3,797,000
Total assets	285,632,000	294,676,000
LIABILITIES AND SHAREHOLDERS' EQUITY (DEFICIT)
Accounts payable	11,365,000	8,562,000
Accrued compensation	11,796,000	11,473,000
Other accrued liabilities	20,465,000	15,767,000
Current portion of deferred lease incentive	837,000	784,000
Current portion of liability related to the sale of future royalties, net	25,880,000	17,779,000
Current portion of deferred revenue	297,000	1,405,000
Total current liabilities	70,640,000	55,770,000
Deferred lease incentive, net of current portion	4,675,000	5,129,000
Deferred revenue, net of current portion	83,710,000	93,752,000
Convertible 4.5% senior notes, net	2,064,000	2,050,000
Liability related to the sale of future royalties, net	122,345,000	151,634,000
Other long-term liabilities	4,180,000	4,236,000
Total liabilities	287,614,000	312,571,000
Shareholders' deficit:
Common stock	1,494,000	1,325,000
Additional paid-in capital	1,192,813,000	1,009,362,000
Accumulated deficit	(1,196,289,000)	(1,028,582,000)
Total shareholders' equity (deficit)	(1,982,000)	(17,895,000)
Total liabilities and shareholders' equity (deficit)	285,632,000	294,676,000
Adjustments due to new guidance | ASU 2014-09
ASSETS
Non-cash royalty receivable		8,900,000
Total current assets		8,900,000
Total assets		8,900,000
LIABILITIES AND SHAREHOLDERS' EQUITY (DEFICIT)
Current portion of deferred revenue		41,000
Total current liabilities		41,000
Deferred revenue, net of current portion		(5,231,000)
Total liabilities		(5,190,000)
Shareholders' deficit:
Accumulated deficit		14,090,000
Total shareholders' equity (deficit)		14,090,000
Total liabilities and shareholders' equity (deficit)		8,900,000
Deferred tax assets:
Increase (decrease) in deferred tax assets		3,900,000
Phase 1 clinical trial | Novartis
Deferred tax assets:
Potential milestone payment	5,000,000
Phase 1 clinical trial | Takeda
Deferred tax assets:
Milestone earned, included in accounts receivable	5,000,000
Phase 1 clinical trial | Adjustments due to new guidance | Takeda | ASU 2014-09
Deferred tax assets:
Potential milestone payment		5,000,000	$ 5,000,000
Technological Improvements
LIABILITIES AND SHAREHOLDERS' EQUITY (DEFICIT)
Deferred revenue, net of current portion	$ 5,900,000	$ 6,800,000
Technological Improvements | Takeda
Deferred tax assets:
Potential milestone payment				$ 400,000

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Impact of Adopting ASC 606, Pro Forma Balance Sheet (Details) - USD ($)	Dec. 31, 2018	Jan. 02, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
ASSETS
Cash and cash equivalents	$ 262,252,000	$ 267,107,000	$ 267,107,000	$ 159,964,000	$ 245,026,000		$ 278,109,000
Accounts receivable	1,701,000	2,649,000	2,649,000
Unbilled revenue	617,000	2,580,000	2,580,000
Contract asset	500,000
Non-cash royalty receivable	9,249,000	8,900,000
Inventory	0	1,038,000	1,038,000
Prepaid and other current assets	4,462,000	2,967,000	2,967,000
Total current assets	278,781,000	285,241,000	276,341,000
Property and equipment, net of accumulated depreciation	12,891,000	14,538,000	14,538,000
Other assets	3,709,000	3,797,000	3,797,000
Total assets	295,381,000	303,576,000	294,676,000
LIABILITIES AND SHAREHOLDERS' EQUITY (DEFICIT)
Accounts payable	11,365,000	8,562,000	8,562,000
Accrued compensation	11,796,000	11,473,000	11,473,000
Other accrued liabilities	20,465,000	15,767,000	15,767,000
Current portion of deferred lease incentive	837,000	784,000	784,000
Current portion of liability related to the sale of future royalties, net	25,880,000	17,779,000	17,779,000
Current portion of deferred revenue	317,000	1,446,000	1,405,000
Total current liabilities	70,660,000	55,811,000	55,770,000
Deferred lease incentive, net of current portion	4,675,000	5,129,000	5,129,000			$ 2,000,000
Deferred revenue, net of current portion	80,485,000	88,521,000	93,752,000
Convertible 4.5% senior notes, net	2,064,000	2,050,000	2,050,000
Liability related to the sale of future royalties, net	122,345,000	151,634,000	151,634,000
Other long-term liabilities	4,180,000	4,236,000	4,236,000
Total liabilities	284,409,000	307,381,000	312,571,000
Shareholders' deficit:
Preferred stock
Common stock	1,494,000	1,325,000	1,325,000
Additional paid-in capital	1,192,813,000	1,009,362,000	1,009,362,000
Accumulated deficit	(1,183,335,000)	(1,014,492,000)	(1,028,582,000)
Total shareholders' equity (deficit)	10,972,000	(3,805,000)	(17,895,000)	$ (152,850,000)	$ (82,304,000)		$ 35,104,000
Total liabilities and shareholders' equity (deficit)	295,381,000	$ 303,576,000	294,676,000
Pro forma as if previous accounting was in effect | ASU 2014-09
ASSETS
Cash and cash equivalents	262,252,000		267,107,000
Accounts receivable	1,701,000		2,649,000
Unbilled revenue	617,000		2,580,000
Inventory			1,038,000
Prepaid and other current assets	4,462,000		2,967,000
Total current assets	269,032,000		276,341,000
Property and equipment, net of accumulated depreciation	12,891,000		14,538,000
Other assets	3,709,000		3,797,000
Total assets	285,632,000		294,676,000
LIABILITIES AND SHAREHOLDERS' EQUITY (DEFICIT)
Accounts payable	11,365,000		8,562,000
Accrued compensation	11,796,000		11,473,000
Other accrued liabilities	20,465,000		15,767,000
Current portion of deferred lease incentive	837,000		784,000
Current portion of liability related to the sale of future royalties, net	25,880,000		17,779,000
Current portion of deferred revenue	297,000		1,405,000
Total current liabilities	70,640,000		55,770,000
Deferred lease incentive, net of current portion	4,675,000		5,129,000
Deferred revenue, net of current portion	83,710,000		93,752,000
Convertible 4.5% senior notes, net	2,064,000		2,050,000
Liability related to the sale of future royalties, net	122,345,000		151,634,000
Other long-term liabilities	4,180,000		4,236,000
Total liabilities	287,614,000		312,571,000
Shareholders' deficit:
Common stock	1,494,000		1,325,000
Additional paid-in capital	1,192,813,000		1,009,362,000
Accumulated deficit	(1,196,289,000)		(1,028,582,000)
Total shareholders' equity (deficit)	(1,982,000)		(17,895,000)
Total liabilities and shareholders' equity (deficit)	$ 285,632,000		$ 294,676,000

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Impact of Adopting ASC 606, Pro Forma Statement of Operations and Comprehensive Loss (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended														6 Months Ended		9 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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016
Revenues:
Total revenues	$ 13,416	$ 10,928	$ 9,287	$ 19,815	$ 39,448	$ 8,480	$ 39,020	$ 28,499	$ 13,846	$ 7,660	$ 7,408	$ 19,714	$ 18,029	$ 14,851	$ 21,506	$ 32,880		$ 53,446	$ 115,447	$ 48,628	$ 60,002
Operating Expenses:
Research and development	43,681	47,243	38,701	44,831	39,843	31,689	35,319	32,888	33,657	32,909	38,652	36,094	38,199	35,132	66,566	73,331		174,456	139,739	141,312	148,077
General and administrative	9,752	8,347	8,652	9,995	9,048	7,908	8,836	8,119	8,536	9,459	9,298	11,235	8,054	8,329	17,995	16,383		36,746	33,911	38,528	36,916
Restructuring charge	406	870	686	1,731	393			386	301	4,130					4,431		$ 2,347	3,693	779	4,431
Total operating expenses	53,839	56,460	48,039	56,557	49,284	39,597	44,155	41,393	42,494	46,498	47,950	47,329	46,253	43,461	88,992	89,714		214,895	174,429	184,271	184,993
Loss from operations	(40,423)	(45,532)	(38,752)	(36,742)	(9,836)	(31,117)	(5,135)	(12,894)	(28,648)	(38,838)	(40,542)	(27,615)	(28,224)	(28,610)	(67,486)	(56,834)		(161,449)	(58,982)	(135,643)	(124,991)
Investment income, net															259	111		4,227	1,146	473	325
Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes	(2,428)	(2,546)	(2,611)	(3,046)	(3,221)	(3,385)	(3,501)	(3,575)	(3,647)	(5,018)	(4,956)	(4,972)	(5,059)	(5,143)	(8,665)	(10,202)		(10,631)	(13,682)	(18,593)	(20,130)
Interest expense on convertible senior notes	(25)	(23)	(23)	(24)	(28)	(762)	(1,125)	(1,125)	(1,099)	(1,150)					(2,249)			(95)	(3,040)	(2,387)	(138)
Other (expense) income, net															(742)	(42)		(895)	1,461	(583)	117
Net loss	$ (41,799)	$ (46,807)	$ (41,624)	$ (38,613)	$ (13,118)	$ (56,682)	$ (8,867)	$ (17,345)	$ (34,152)	$ (44,731)	$ (45,922)	$ (31,928)	$ (33,227)	$ (33,740)	$ (78,883)	$ (66,967)		$ (168,843)	$ (96,012)	$ (156,733)	$ (144,817)
Basic and diluted net loss per common share (in dollar per share)	$ (0.28)	$ (0.32)	$ (0.31)	$ (0.30)	$ (0.11)	$ (0.61)	$ (0.10)	$ (0.20)	$ (0.39)	$ (0.51)	$ (0.53)	$ (0.37)	$ (0.38)	$ (0.39)	$ (0.91)	$ (0.77)		$ (1.21)	$ (0.98)	$ (1.80)	$ (1.67)
Pro forma as if previous accounting was in effect | ASU 2014-09
Revenues:
Total revenues																		$ 54,582
Operating Expenses:
Research and development																		174,456
General and administrative																		36,746
Restructuring charge																		3,693
Total operating expenses																		214,895
Loss from operations																		(160,313)
Investment income, net																		4,227
Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes																		(10,631)
Interest expense on convertible senior notes																		(95)
Other (expense) income, net																		(895)
Net loss																		$ (167,707)
Basic and diluted net loss per common share (in dollar per share)																		$ (1.20)
Adjustments due to new guidance | ASU 2014-09
Revenues:
Total revenues																		$ 5,000
License and milestone fees
Revenues:
Total revenues	$ 1,747	$ 672	$ 1,321	$ 11,540	$ 29,580	$ 79	$ 31,080	$ 18,730	$ 5,076	$ 76	$ 76	$ 10,077	$ 10,692	$ 6,070	$ 5,152	$ 16,762		15,280	$ 79,469	$ 15,305	$ 26,915
License and milestone fees | Pro forma as if previous accounting was in effect | ASU 2014-09
Revenues:
Total revenues																		16,765
License and milestone fees | Adjustments due to new guidance | ASU 2014-09
Operating Expenses:
Potential milestone payment	5,000																$ 5,000	5,000
Non-cash royalty revenue related to the sale of future royalties
Revenues:
Total revenues	9,281	8,441	7,242	7,190	7,587	6,503	6,439	7,613	6,710	6,184	5,944	7,380	6,291	5,684	12,894	11,975		32,154	28,142	26,218	25,299
Non-cash royalty revenue related to the sale of future royalties | Pro forma as if previous accounting was in effect | ASU 2014-09
Revenues:
Total revenues																		31,805
Research and development support
Revenues:
Total revenues	218	388	388	383	452	650	902	1,478	1,427	1,354	1,335	1,059	848	772	2,781	1,620		1,377	3,482	5,175	4,014
Research and development support | Pro forma as if previous accounting was in effect | ASU 2014-09
Revenues:
Total revenues																		1,377
Clinical materials revenue
Revenues:
Total revenues	$ 2,170	$ 1,427	$ 336	$ 702	$ 1,829	$ 1,248	$ 599	$ 678	$ 633	$ 46	$ 53	$ 1,198	$ 3	$ 2,325	$ 679	$ 2,328		4,635	$ 4,354	$ 1,930	$ 3,579
Clinical materials revenue | Pro forma as if previous accounting was in effect | ASU 2014-09
Revenues:
Total revenues																		$ 4,635

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Revenue Recognition (Details)	1 Months Ended						12 Months Ended
	Oct. 31, 2018item	Dec. 31, 2015item	Mar. 31, 2015USD ($)item	Oct. 31, 2013	May 31, 2013item	Mar. 31, 2013item	Dec. 31, 2018USD ($)item	Dec. 31, 2011item	Dec. 31, 2010item	Dec. 31, 2000USD ($)item	Jan. 31, 2014USD ($)
Minimum
Summary of Significant Accounting Policies
Period to earn royalty payments							10 years
Maximum
Summary of Significant Accounting Policies
Period to earn royalty payments							12 years
Amgen/Oxford BioTherapeutics
Summary of Significant Accounting Policies
Number of single-target licenses		4			1					3
Bayer
Summary of Significant Accounting Policies
Number of single-target licenses							1
Biotest
Summary of Significant Accounting Policies
Number of single-target licenses							1
CytomX
Summary of Significant Accounting Policies
Number of single-target licenses							1
Potential milestone payment | $											$ 160,000,000
Fusion Pharmaceuticals
Summary of Significant Accounting Policies
Number of single-target licenses							1
Potential milestone payment | $							$ 500,000
Lilly
Summary of Significant Accounting Policies
Number of single-target licenses	3							3
Novartis
Summary of Significant Accounting Policies
Number of single-target licenses						1	5		6
Term of agreement				1 year					3 years
Roche
Summary of Significant Accounting Policies
Number of single-target licenses							5
Roche | Undisclosed Target
Summary of Significant Accounting Policies
Potential milestone payment | $										$ 38,000,000
Sanofi
Summary of Significant Accounting Policies
Number of single-target licenses							5
Takeda
Summary of Significant Accounting Policies
Number of single-target licenses							1
Term of agreement			3 years
Potential milestone payment | $			$ 210,000,000
Takeda | Maximum
Summary of Significant Accounting Policies
Number of single-target licenses			2

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Performance Obligations Comprising Deferred Revenue (Details) $ in Millions	Dec. 31, 2018USD ($)
Summary of Significant Accounting Policies
Revenue, Remaining Performance Obligation	$ 80.8

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Performance Obligations (Details)	Dec. 31, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Summary of Significant Accounting Policies
Remaining performance obligations, percent	0.40%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Summary of Significant Accounting Policies
Remaining performance obligations, percent	1.60%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction	48 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Summary of Significant Accounting Policies
Remaining performance obligations, percent	98.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction	60 months

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Contract Balances (Details) - USD ($)	1 Months Ended	3 Months Ended														6 Months Ended		12 Months Ended
	Dec. 31, 2018	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	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2015	Jan. 31, 2014
Changes in the Company's contract assets and contract liabilities
Contract asset, Additions																		$ 500,000
Contract asset, Deductions																		(5,000,000)
Contract Asset, Impact Of Netting	$ 5,000,000	$ 5,000,000																5,000,000
Contract asset, Balance at End of Period	500,000	500,000																500,000
Contract liabilities:
Deferred revenue, Additions																		730,000
Deferred revenue, Deductions																		(14,895,000)
Contract Liabilities, Impact Of Netting	5,000,000	5,000,000																5,000,000
Contract liabilities, Balance at End of Period	80,802,000	80,802,000																80,802,000
Revenues recognized from changes in contract asset and liability balances
Amounts included in contract liabilities at the beginning of the period																		14,139,000
Performance obligations satisfied in previous periods																		1,476,000
Revenue from contract with customer		13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Milestone recognized as contract asset																		500,000
Clinical materials revenue
Revenues recognized from changes in contract asset and liability balances
Revenue from contract with customer		2,170,000	$ 1,427,000	$ 336,000	$ 702,000	$ 1,829,000	$ 1,248,000	$ 599,000	$ 678,000	$ 633,000	46,000	53,000	$ 1,198,000	$ 3,000	$ 2,325,000	679,000	$ 2,328,000	4,635,000	$ 4,354,000	$ 1,930,000	3,579,000
Takeda
Contract liabilities:
Deferred revenue, Deductions																		(5,900,000)
Revenues recognized from changes in contract asset and liability balances
Potential milestone payment																						$ 210,000,000
Debiopharm | Technological Improvements
Revenues recognized from changes in contract asset and liability balances
Amortization of deferred revenue																		2,100,000
Debiopharm and another collaborator
Revenues recognized from changes in contract asset and liability balances
Deferred revenue recognized upon completion of performance obligations																		750,000
CytomX
Contract liabilities:
Contract liabilities, Balance at Beginning of Period											$ 13,000,000					$ 13,000,000
Contract liabilities, Balance at End of Period												$ 13,000,000									$ 13,000,000
Revenues recognized from changes in contract asset and liability balances
Potential milestone payment																							$ 160,000,000
Fusion Pharmaceuticals
Revenues recognized from changes in contract asset and liability balances
Potential milestone payment	500,000	$ 500,000																500,000
Amgen/Oxford BioTherapeutics
Revenues recognized from changes in contract asset and liability balances
Revenue from contract with customer																		4,000,000
Amgen/Oxford BioTherapeutics | Development milestones
Revenues recognized from changes in contract asset and liability balances
Milestone earned, included in accounts receivable	$ 1,000,000
Upon shipment | Other Collaborator | Clinical materials revenue
Revenues recognized from changes in contract asset and liability balances
Revenue from contract with customer																		335,000
Adjustments due to new guidance | ASU 2014-09
Revenues recognized from changes in contract asset and liability balances
Revenue from contract with customer																		5,000,000
Pro forma as if previous accounting was in effect | ASU 2014-09
Revenues recognized from changes in contract asset and liability balances
Revenue from contract with customer																		54,582,000
Pro forma as if previous accounting was in effect | ASU 2014-09 | Clinical materials revenue
Revenues recognized from changes in contract asset and liability balances
Revenue from contract with customer																		4,635,000
Right-to-test agreement | Takeda
Revenues recognized from changes in contract asset and liability balances
Amounts included in contract liabilities at the beginning of the period																		$ 10,900,000
Potential milestone payment																						$ 4,000,000

Summary of Significant Accou_12

Summary of Significant Accounting Policies - Financial Instruments (Details)	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jan. 02, 2018USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)
Financial Instruments and Concentration of Credit Risk
Number of financial institutions in the U.S. in which cash and cash equivalents are primarily maintained	3
Marketable securities held by entity	$ 0	$ 0
Cash and Cash Equivalents
Cash and cash equivalents	262,252,000	267,107,000	$ 267,107,000	$ 159,964,000	$ 245,026,000	$ 278,109,000
Noncash Investing Activities
Accrued capital expenditures	$ 715,000	$ 482,000

Summary of Significant Accou_13

Summary of Significant Accounting Policies - Fair Value (Details) - USD ($)	6 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016	Jun. 30, 2016
Fair value hierarchy for the Company's financial assets measured at fair value
Interest rate (as a percent)			4.50%
Recurring basis
Fair value hierarchy for the Company's financial assets measured at fair value
Cash equivalents	$ 240,013,000	$ 240,013,000	$ 242,604,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value hierarchy for the Company's financial assets measured at fair value
Cash equivalents	$ 240,013,000	$ 240,013,000	242,604,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Estimated fair value
Fair value hierarchy for the Company's financial assets measured at fair value
Convertible debt fair value			$ 2,800,000
Convertible Notes
Fair value hierarchy for the Company's financial assets measured at fair value
Interest rate (as a percent)	4.50%	4.50%	4.50%	4.50%
Principal amount of debt for conversion calculations	$ 1,000	$ 1,000			$ 1,000
Debt converted	$ 97,900,000	96,900,000
Shares issued with debt conversion (in shares)	26,160,187
Convertible Notes | Significant Other Observable Inputs (Level 2) | Face Value
Fair value hierarchy for the Company's financial assets measured at fair value
Convertible debt fair value	$ 2,100,000	2,100,000	$ 2,100,000
Convertible Notes | Significant Other Observable Inputs (Level 2) | Estimated fair value
Fair value hierarchy for the Company's financial assets measured at fair value
Convertible debt fair value	$ 3,800,000	$ 3,800,000

Summary of Significant Accou_14

Summary of Significant Accounting Policies - Inventory (Details) - USD ($)	3 Months Ended														6 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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Jan. 02, 2018
Inventory
Raw materials					$ 40,000													$ 40,000
Work in process					998,000													998,000
Total	$ 0				1,038,000												$ 0	1,038,000			$ 1,038,000
Minimum supply period of raw materials that is not supported by firm, fixed orders and/or projections from collaborators considered to expense inventory																	12 years
Value of excess inventory	0																$ 0
Expense related to excess inventory	$ 43,681,000	$ 47,243,000	$ 38,701,000	$ 44,831,000	$ 39,843,000	$ 31,689,000	$ 35,319,000	$ 32,888,000	$ 33,657,000	$ 32,909,000	$ 38,652,000	$ 36,094,000	$ 38,199,000	$ 35,132,000	$ 66,566,000	$ 73,331,000	$ 174,456,000	139,739,000	$ 141,312,000	$ 148,077,000
Raw materials inventory write-downs																		1,100,000
Rolling period of firm, fixed orders for conjugate that the company is required to manufacture																	6 months
Rolling period of manufacturing projections for the quantity of conjugate the collaborator expects to need																	12 months
Maximum period of firm, fixed orders and/or projections from collaborators considered for capitalizing inventory																	12 months
Charges to research and development expense related to raw material inventory identified as excess															$ 150,000		$ 0	$ 403,000		$ 1,100,000

Summary of Significant Accou_15

Summary of Significant Accounting Policies - Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 02, 2018	Dec. 31, 2017
Other Accrued Liabilities
Accrued contract payments	$ 6,389		$ 4,901
Accrued clinical trial costs	11,087		8,400
Accrued professional services	1,171		723
Accrued employee benefits	651		574
Accrued public reporting charges	164		156
Other current accrued liabilities	1,003		1,013
Total	20,465	$ 15,767	15,767
Deferred revenue, net of current portion	80,485	$ 88,521	93,752
Technological Improvements
Other Accrued Liabilities
Deferred revenue, net of current portion	$ 5,900		$ 6,800

Summary of Significant Accou_16

Summary of Significant Accounting Policies - PPE (Details) - USD ($)	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Property and Equipment
(Losses) gains on the sale/disposal of furniture and equipment (in dollars)	$ (1,130,000)	$ (115,000)	$ (239,000)	$ 21,000
Leasehold impairment charge	970,000		180,000
Impairment of long-lived assets		$ 0
Machinery and equipment
Property and Equipment
Estimated useful lives		5 years
Computer hardware and software
Property and Equipment
Estimated useful lives		3 years
Furniture and fixtures
Property and Equipment
Estimated useful lives		5 years
(Losses) gains on the sale/disposal of furniture and equipment (in dollars)	$ (1,100,000)	$ (115,000)	$ (239,000)	$ 21,000
Leasehold improvements | Maximum
Property and Equipment
Estimated useful lives		7 years

Summary of Significant Accou_17

Summary of Significant Accounting Policies - Net Loss per Common Share and Stock-Based Compensation (Details)	Jun. 20, 2018shares	Sep. 30, 2018USD ($)shares	Jun. 30, 2018shares	Jun. 30, 2017$ / sharesshares	Feb. 28, 2017$ / sharesshares	Aug. 31, 2016$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2018USD ($)item$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Jun. 30, 2016USD ($)$ / sharesshares	Jun. 30, 2015$ / sharesshares
Computation of Net Loss per Common Share
Options outstanding to purchase common stock, shares issuable under the employee stock purchase plan, and unvested restricted stock at end of period								13,878,000	17,380,000	14,290,000	11,919,000
Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock								1,000	3,001,000	1,579,000	735,000
Shares issuable upon conversion of convertible notes at end of period (in shares)								23,878	501	501	23,878
Common stock equivalents under if-converted method for convertible notes (in shares)								23,878,000	501,000	501,000	718,000
Stock-Based Compensation
Number of employee share-based compensation plans | item									1
Weighted-Average Remaining Life (in years)
Outstanding at the end of the period								6 years 6 months 18 days	6 years 5 months 16 days	6 years 2 months 1 day	6 years 9 months 26 days	6 years 9 months 4 days
Vested or unvested and expected to vest at the end of the period								6 years 6 months 7 days	6 years 5 months 5 days	6 years 1 month 24 days	6 years 9 months 4 days
Exercisable at the end of the period								4 years 8 months 12 days	4 years 5 months 12 days	4 years 11 months 19 days	5 years 3 months 18 days
Aggregate Intrinsic Value
Outstanding at the end of the period | $							$ 13,513,000	$ 23,000	$ 5,818,000	$ 13,513,000
Vested or unvested and expected to vest at the end of the period | $							13,283,000	22,000	5,781,000	13,283,000
Exercisable at the end of the period | $							$ 3,733,000		$ 3,122,000	3,733,000
Additional disclosure for options
Aggregate number of common shares reserved for future issuance									24,700,000
Cash received for exercise of stock options | $									$ 4,301,000	650,000	$ 5,161,000
Stock compensation expense (reduction) | $								8,100,000	16,400,000	11,100,000	21,900,000
Estimated fair value of unvested employee awards, net of estimated forfeitures | $									$ 28,000,000
Weighted average vesting period of unvested employee awards									2 years
Total fair value of options vested | $								$ 17,121,000	$ 7,496,000	10,964,000	15,298,000
Total intrinsic value of options exercised | $									$ 3,787,000	$ 598,000	$ 3,142,000
ESPP
Weighted-average assumptions used to estimate the fair value of each stock option
Dividend (as a percent)									0.00%
Volatility (as a percent)									70.10%
Risk-free interest rate (as a percent)									2.14%
Expected life									6 months
Weighted-Average Grant Date Fair Value
Awarded (in dollars per share) | $ / shares									$ 3.55
Additional disclosure for options
Aggregate number of common shares reserved for future issuance			1,000,000
Threshold period of continuous employment per year			3 months
Threshold period of customary employment in calendar year			5 months
Threshold period of customary employment per week			140 days
Purchase price of common stock (as a Percent)			85.00%
Plan Purchase Period			6 months
Maximum Percentage Of Periodic Payroll Deductions (as a percent)			15.00%
Shares issued to participating employees									205,000
Stock options
Weighted-average assumptions used to estimate the fair value of each stock option
Dividend (as a percent)								0.00%	0.00%	0.00%	0.00%
Volatility (as a percent)								65.63%	71.02%	67.34%	66.34%
Risk-free interest rate (as a percent)								1.29%	2.73%	2.00%	1.80%
Expected life								6 years 3 months 18 days	6 years	6 years	6 years 3 months 18 days
Weighted-average grant date fair value (in dollars per share) | $ / shares								$ 1.76	$ 6.70	$ 1.98	$ 8.91
Number of Stock Options
Outstanding at the beginning of the period (in shares)								11,813,000	11,971,000	13,679,000	9,689,000
Granted (in shares)								3,536,000	5,513,000	1,589,000	3,340,000
Exercised (in shares)									(742,000)	(191,000)	(555,000)
Forfeited/Canceled (in shares)								(1,670,000)	(1,178,000)	(3,106,000)	(661,000)
Outstanding at the end of the period (in shares)							11,971,000	13,679,000	15,564,000	11,971,000	11,813,000	9,689,000
Vested or unvested and expected to vest at the end of the period (in shares)							11,881,000	13,516,000	15,386,000	11,881,000	11,475,000
Exercisable at the end of the period (in shares)							7,996,000	7,898,000	8,405,000	7,996,000	6,453,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share) | $ / shares								$ 13.03	$ 9.92	$ 10.70	$ 12.49
Granted (in dollars per share) | $ / shares								2.90	10.36	3.21	14.34
Exercised (in dollars per share) | $ / shares									4.67	3.42	9.30
Forfeited/Canceled (in dollars per share) | $ / shares								10.64	11.49	10.33	14.84
Outstanding at the end of the period (in dollars per share) | $ / shares							$ 9.92	10.70	10.20	9.92	13.03	$ 12.49
Vested or unvested and expected to vest at the end of the period (in dollars per share) | $ / shares							9.96	10.76	10.21	9.96	13.05
Exercisable at the end of the period (in dollars per share) | $ / shares							$ 12.16	$ 13.15	$ 11.47	$ 12.16	$ 12.63
Additional disclosure for options
Cash received for exercise of stock options | $									$ 3,500,000
Stock options | Chief Executive Officer
Additional disclosure for options
Stock compensation cost due to modification | $								$ 0	$ 116,000	$ 742,000	$ 3,100,000
Performance shares
Stock-Based Compensation
Vesting period		5 years
Number of vesting installments		2
Number of Stock Options
Granted (in shares)		295,200
Aggregate Intrinsic Value
Vested or unvested and expected to vest at the end of the period | $		$ 1,800,000
Restricted stock
Number of Restricted Stock
Unvested at the beginning of the period (in shares)								106,000	2,319,000	199,000	50,000
Awarded (in shares)								118,000		2,253,000	75,000
Vested (in shares)									(503,000)	(25,000)	(19,000)
Forfeited (in shares)								(25,000)		(108,000)
Unvested at the end of the period (in shares)							2,319,000	199,000	1,816,000	2,319,000	106,000	50,000
Weighted-Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share) | $ / shares								$ 6.54	$ 2.82	$ 4.41	$ 9.23
Awarded (in dollars per share) | $ / shares								3.15		2.71	5.65
Vested (in dollars per share) | $ / shares									2.64	5.87	10.13
Forfeited (in dollars per share) | $ / shares								7.52		2.68
Unvested at the end of the period (in dollars per share) | $ / shares							$ 2.82	$ 4.41	$ 2.87	$ 2.82	$ 6.54	$ 9.23
Restricted stock | Officers
Stock-Based Compensation
Number of equal installments restrictions lapse				3	3	3
Service period				5 years	5 years	5 years
Number of Restricted Stock
Awarded (in shares)				239,000	529,830	117,800
Forfeited (in shares)							(71,380)
Weighted-Average Grant Date Fair Value
Awarded (in dollars per share) | $ / shares				$ 4.71	$ 2.47	$ 3.15
Additional disclosure for options
Estimated fair value of unvested employee awards, net of estimated forfeitures | $									$ 2,600,000
Deferred share units
Additional disclosure for options
Stock compensation expense (reduction) | $								$ 215,000	$ 361,000	$ 206,000	$ 380,000
2016 Plan | Stock options
Weighted-average assumptions used to estimate the fair value of each stock option
Number of group of awards for which expected term is calculated for and applied									1
2016 Plan | Stock options | Maximum
Stock-Based Compensation
Vesting period									4 years
Exercise period									10 years
2018 Plan
Computation of Net Loss per Common Share
Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock	7,500,000
Stock-Based Compensation
Common stock authorized for issuance (in shares)	19,500,000
2018 Plan | Stock options
Number of Stock Options
Exercised (in shares)									(742,000)

Summary of Significant Accou_18

Summary of Significant Accounting Policies - Segments (Details)	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Segment Information
Number of operating segments		1
Bayer | Revenues percentage | Customer concentration
Segment Information
Percentages of revenue recognized				17.00%
CytomX | Revenues percentage | Customer concentration
Segment Information
Percentages of revenue recognized		8.00%	13.00%
Debiopharm | Revenues percentage | Customer concentration
Segment Information
Percentages of revenue recognized		2.00%	26.00%
Lilly | Revenues percentage | Customer concentration
Segment Information
Percentages of revenue recognized	4.00%	2.00%	1.00%	11.00%
Novartis | Revenues percentage | Customer concentration
Segment Information
Percentages of revenue recognized	24.00%	2.00%		1.00%
Roche | Revenues percentage | Customer concentration
Segment Information
Percentages of revenue recognized	60.00%	60.00%	24.00%	43.00%
Sanofi | Revenues percentage | Customer concentration
Segment Information
Percentages of revenue recognized			31.00%
Takeda | Revenues percentage | Customer concentration
Segment Information
Percentages of revenue recognized	8.00%	23.00%	4.00%	16.00%

Summary of Significant Accou_19

Summary of Significant Accounting Policies - Recently issued accounting pronouncements (Details) - ASU 2016-2 - Restatement Adjustment $ in Millions	Jan. 01, 2019USD ($)
Minimum
Recent Accounting Pronouncements
Right-of-use assets	$ 16
Lease liabilities	16
Maximum
Recent Accounting Pronouncements
Right-of-use assets	19
Lease liabilities	$ 19

Agreements - Roche (Details)

Agreements - Roche (Details) $ in Thousands	1 Months Ended		3 Months Ended														6 Months Ended		12 Months Ended
	Jan. 31, 2019USD ($)	May 31, 2000	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2000USD ($)item
Collaborative Agreements disclosures
Revenue from contract with customer			$ 13,416	$ 10,928	$ 9,287	$ 19,815	$ 39,448	$ 8,480	$ 39,020	$ 28,499	$ 13,846	$ 7,660	$ 7,408	$ 19,714	$ 18,029	$ 14,851	$ 21,506	$ 32,880	$ 53,446	$ 115,447	$ 48,628	$ 60,002
Non-cash royalty revenue related to sale of future royalties																	12,894		32,154	28,142		25,299
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer			1,747	$ 672	$ 1,321	$ 11,540	$ 29,580	$ 79	$ 31,080	$ 18,730	$ 5,076	$ 76	$ 76	$ 10,077	10,692	$ 6,070	5,152	16,762	15,280	79,469	$ 15,305	26,915
Royalty revenue
Collaborative Agreements disclosures
Revenue from contract with customer															$ 195			$ 195				195
Roche
Collaborative Agreements disclosures
Period in arrears to receive royalty reports and payments related to sales of Kadcyla		3 months
Roche | Upfront payment
Collaborative Agreements disclosures
Revenue from contract with customer																							$ 2,000
Roche | License and milestone fees
Collaborative Agreements disclosures
Potential milestone payment																							44,000
Roche | Royalty revenue
Collaborative Agreements disclosures
Revenue from contract with customer																	$ 12,900		32,200	$ 28,100		$ 25,300
Roche | Kadcyla | Development milestones
Collaborative Agreements disclosures
Revenue from contract with customer																			13,500
Potential milestone payment																							13,500
Roche | Kadcyla | Regulatory milestones
Collaborative Agreements disclosures
Revenue from contract with customer																			20,500
Potential milestone payment			5,000																5,000				30,500
Roche | Undisclosed Target
Collaborative Agreements disclosures
Revenue from contract with customer																							1,000
Potential milestone payment																							$ 38,000
Number of undisclosed targets with exclusive licenses | item																							4
Roche | Undisclosed Target | Development milestones
Collaborative Agreements disclosures
Potential milestone payment																							$ 8,000
Roche | Undisclosed Target | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payment																							20,000
Roche | Undisclosed Target | Milestone payments
Collaborative Agreements disclosures
Potential milestone payment																							$ 10,000
Roche | Undisclosed Target | IND application filed
Collaborative Agreements disclosures
Potential milestone payment			$ 1,000																$ 1,000
OMERS | Kadcyla | Subsequent event
Collaborative Agreements disclosures
Non-cash royalty revenue related to sale of future royalties	$ 65,200

Agreements - Amgen_Oxford BioTh

Agreements - Amgen/Oxford BioTherapeutics (Details)	1 Months Ended						3 Months Ended														6 Months Ended		12 Months Ended
	Dec. 31, 2018USD ($)	Aug. 31, 2018item	Feb. 29, 2016item	Dec. 31, 2015item	Oct. 31, 2013USD ($)	May 31, 2013USD ($)item	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2000USD ($)item
Collaborative Agreements disclosures
Revenue from contract with customer							$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Amgen/Oxford BioTherapeutics
Collaborative Agreements disclosures
Revenue from contract with customer																							4,000,000
Number of single-target licenses | item				4		1																					3
Number of licenses terminated | item		1	2
Amgen/Oxford BioTherapeutics | Development milestones
Collaborative Agreements disclosures
Potential milestone payment					$ 9,000,000
Amgen/Oxford BioTherapeutics | IND application filed
Collaborative Agreements disclosures
Revenue from contract with customer	$ 1,000,000
Amgen/Oxford BioTherapeutics | Phase 2 clinical trial
Collaborative Agreements disclosures
Potential milestone payment	$ 3,000,000						3,000,000																3,000,000
Amgen/Oxford BioTherapeutics | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payment					20,000,000
Amgen/Oxford BioTherapeutics | Milestone payments
Collaborative Agreements disclosures
Potential milestone payment					5,000,000
Upfront payment | Amgen/Oxford BioTherapeutics
Collaborative Agreements disclosures
Revenue from contract with customer																											$ 1,000,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer							1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
License and milestone fees | Amgen/Oxford BioTherapeutics
Collaborative Agreements disclosures
Revenue from contract with customer					500,000	$ 500,000																	84,000
Potential milestone payment					$ 34,000,000
License and milestone fees | Amgen/Oxford BioTherapeutics | IND application filed
Collaborative Agreements disclosures
Revenue from contract with customer																										1,000,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer							$ 218,000	$ 388,000	$ 388,000	$ 383,000	$ 452,000	$ 650,000	$ 902,000	$ 1,478,000	$ 1,427,000	$ 1,354,000	$ 1,335,000	$ 1,059,000	$ 848,000	$ 772,000	2,781,000	$ 1,620,000	1,377,000	3,482,000	$ 5,175,000	4,014,000
Costs of services and materials																					$ 22,000
Research and development support | Amgen/Oxford BioTherapeutics
Collaborative Agreements disclosures
Costs of services and materials																							$ 0	$ 0		$ 15,000

Agreements - Sanofi (Details)

Agreements - Sanofi (Details) $ in Thousands	1 Months Ended	3 Months Ended														6 Months Ended		12 Months Ended
	May 31, 2017item	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, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)
Collaborative Agreements disclosures
Revenue from contract with customer		$ 13,416	$ 10,928	$ 9,287	$ 19,815	$ 39,448	$ 8,480	$ 39,020	$ 28,499	$ 13,846	$ 7,660	$ 7,408	$ 19,714	$ 18,029	$ 14,851	$ 21,506	$ 32,880	$ 53,446	$ 115,447	$ 48,628	$ 60,002
Sanofi
Collaborative Agreements disclosures
Number of compounds | item	4
Sanofi | Development milestones
Collaborative Agreements disclosures
Revenue from contract with customer																		26,500
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer		$ 1,747	$ 672	$ 1,321	$ 11,540	$ 29,580	$ 79	$ 31,080	$ 18,730	$ 5,076	$ 76	$ 76	$ 10,077	$ 10,692	$ 6,070	$ 5,152	$ 16,762	$ 15,280	79,469	$ 15,305	$ 26,915
License and milestone fees | Sanofi
Collaborative Agreements disclosures
Revenue from contract with customer																			30,000
License and milestone fees | Sanofi | Development milestones
Collaborative Agreements disclosures
Revenue from contract with customer																			6,000
License amendments | Sanofi
Collaborative Agreements disclosures
Revenue from contract with customer																			$ 30,000

Agreements - Biotest (Details)

Agreements - Biotest (Details) - USD ($)	1 Months Ended	3 Months Ended														6 Months Ended		12 Months Ended
	Sep. 30, 2008	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	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2006
Collaborative Agreements disclosures
Revenue from contract with customer		$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Biotest | Development milestones
Collaborative Agreements disclosures
Potential milestone payment																						$ 4,500,000
Biotest | Phase IIb Clinical Trial
Collaborative Agreements disclosures
Potential milestone payment		2,000,000																2,000,000
Biotest | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payment																						31,000,000
Biotest | Milestone payments
Collaborative Agreements disclosures
Revenue from contract with customer	$ 500,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer		1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
License and milestone fees | Biotest
Collaborative Agreements disclosures
Potential milestone payment																						35,500,000
Upfront payment | Biotest
Collaborative Agreements disclosures
Revenue from contract with customer																						$ 1,000,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer		218,000	388,000	388,000	383,000	452,000	650,000	902,000	1,478,000	1,427,000	1,354,000	1,335,000	1,059,000	848,000	772,000	2,781,000	1,620,000	1,377,000	3,482,000	5,175,000	4,014,000
Costs of services and materials																22,000
Research and development support | Biotest
Collaborative Agreements disclosures
Costs of services and materials																22,000		50,000	41,000		160,000
Clinical materials revenue
Collaborative Agreements disclosures
Revenue from contract with customer		$ 2,170,000	$ 1,427,000	$ 336,000	$ 702,000	$ 1,829,000	$ 1,248,000	$ 599,000	$ 678,000	$ 633,000	$ 46,000	$ 53,000	$ 1,198,000	$ 3,000	$ 2,325,000	679,000	$ 2,328,000	4,635,000	$ 4,354,000	$ 1,930,000	3,579,000
Clinical materials revenue | Biotest
Collaborative Agreements disclosures
Costs of services and materials																$ 549,000		$ 0			$ 1,800,000

Agreements - Bayer (Details)

Agreements - Bayer (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended														6 Months Ended		12 Months Ended
	Jan. 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	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2008
Collaborative Agreements disclosures
Total revenues		$ 13,416	$ 10,928	$ 9,287	$ 19,815	$ 39,448	$ 8,480	$ 39,020	$ 28,499	$ 13,846	$ 7,660	$ 7,408	$ 19,714	$ 18,029	$ 14,851	$ 21,506	$ 32,880	$ 53,446	$ 115,447	$ 48,628	$ 60,002
Bayer | Minimum
Collaborative Agreements disclosures
Percentage of royalty payments																						4.00%
Bayer | Maximum
Collaborative Agreements disclosures
Percentage of royalty payments																						7.00%
Bayer | Development milestones
Collaborative Agreements disclosures
Potential milestone payment		2,000																2,000				$ 16,000
Bayer | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payment		6,000																6,000				44,500
Bayer | Milestone payments
Collaborative Agreements disclosures
Potential milestone payment																						110,000
Upfront payment | Bayer
Collaborative Agreements disclosures
Total revenues																						4,000
License and milestone fees
Collaborative Agreements disclosures
Total revenues		$ 1,747	$ 672	$ 1,321	$ 11,540	$ 29,580	$ 79	$ 31,080	$ 18,730	$ 5,076	$ 76	$ 76	$ 10,077	$ 10,692	$ 6,070	$ 5,152	$ 16,762	15,280	$ 79,469	$ 15,305	$ 26,915
License and milestone fees | Bayer
Collaborative Agreements disclosures
Total revenues																		$ 13,000
Potential milestone payment																						$ 170,500
License and milestone fees | Bayer | Phase 2 clinical trial
Collaborative Agreements disclosures
Total revenues	$ 10,000

Agreements - Novartis (Details)

Agreements - Novartis (Details)	1 Months Ended			3 Months Ended														6 Months Ended		12 Months Ended
	Oct. 31, 2014USD ($)item	Oct. 31, 2013USD ($)	Mar. 31, 2013USD ($)item	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2018USD ($)item	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2010USD ($)item	May 31, 2015USD ($)	Jan. 31, 2015USD ($)
Collaborative Agreements disclosures
Revenue from contract with customer				$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Novartis
Collaborative Agreements disclosures
Number of single-target licenses | item			1																	5				6
Term of agreement		1 year																						3 years
Number of related targets | item			2
Number of remaining licenses | item	3
Novartis | Right-to-test agreement
Collaborative Agreements disclosures
Revenue from contract with customer		$ 5,000,000
Novartis | License amendments
Collaborative Agreements disclosures
Revenue from contract with customer			$ 3,500,000
Novartis | Development milestones
Collaborative Agreements disclosures
Potential milestone payment																								$ 22,500,000	$ 5,000,000	$ 5,000,000
Novartis | Phase 1 clinical trial
Collaborative Agreements disclosures
Revenue from contract with customer																					5,000,000
Potential milestone payment				5,000,000																$ 5,000,000
Novartis | Phase 2 clinical trial
Collaborative Agreements disclosures
Potential milestone payment				7,500,000																7,500,000
Novartis | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payment																								77,000,000
Novartis | Milestone payments
Collaborative Agreements disclosures
Potential milestone payment	$ 199,500,000																							100,000,000
Upfront payment | Novartis
Collaborative Agreements disclosures
Revenue from contract with customer	$ 1,000,000		$ 1,000,000																					45,000,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer				1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
License and milestone fees | Novartis
Collaborative Agreements disclosures
Revenue from contract with customer																				978,000
Potential milestone payment																								199,500,000
Exercise fee | Novartis
Collaborative Agreements disclosures
Revenue from contract with customer																								$ 1,000,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer				$ 218,000	$ 388,000	$ 388,000	$ 383,000	$ 452,000	$ 650,000	$ 902,000	$ 1,478,000	$ 1,427,000	$ 1,354,000	$ 1,335,000	$ 1,059,000	$ 848,000	$ 772,000	2,781,000	$ 1,620,000	1,377,000	3,482,000	$ 5,175,000	4,014,000
Costs of services and materials																		22,000
Research and development support | Novartis
Collaborative Agreements disclosures
Costs of services and materials																		$ 17,000		$ 0	$ 32,000		$ 67,000

Agreements - Lilly (Details)

Agreements - Lilly (Details)	1 Months Ended	3 Months Ended														6 Months Ended		12 Months Ended
	Oct. 31, 2018item	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, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2011USD ($)item	Jan. 02, 2018USD ($)
Collaborative Agreements disclosures
Revenue from contract with customer		$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Remaining arrangement consideration to be recognized as license revenue		80,485,000				93,752,000												80,485,000	93,752,000						$ 88,521,000
Expense related to excess inventory		43,681,000	47,243,000	38,701,000	44,831,000	39,843,000	31,689,000	35,319,000	32,888,000	33,657,000	32,909,000	38,652,000	36,094,000	38,199,000	35,132,000	66,566,000	73,331,000	174,456,000	139,739,000	141,312,000	148,077,000
Lilly
Collaborative Agreements disclosures
Number of development and commercialization licenses | item	3																							3
Lilly | Phase 1 clinical trial
Collaborative Agreements disclosures
Revenue from contract with customer																					5,000,000
Upfront payment | Lilly
Collaborative Agreements disclosures
Revenue from contract with customer																								$ 20,000,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer		1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
License and milestone fees | Lilly
Collaborative Agreements disclosures
Revenue from contract with customer																		692,000
License and milestone fees | Lilly | Phase 1 clinical trial
Collaborative Agreements disclosures
Revenue from contract with customer																					5,000,000
Exercise fee | Lilly
Collaborative Agreements disclosures
Revenue from contract with customer																						$ 2,000,000	$ 2,000,000	$ 2,000,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer		218,000	388,000	388,000	383,000	452,000	650,000	902,000	1,478,000	1,427,000	1,354,000	1,335,000	1,059,000	848,000	772,000	2,781,000	1,620,000	1,377,000	3,482,000	5,175,000	4,014,000
Costs of services and materials																22,000
Research and development support | Lilly
Collaborative Agreements disclosures
Costs of services and materials																46,000		24,000	74,000		182,000
Clinical materials revenue
Collaborative Agreements disclosures
Revenue from contract with customer		$ 2,170,000	$ 1,427,000	$ 336,000	$ 702,000	$ 1,829,000	$ 1,248,000	$ 599,000	$ 678,000	$ 633,000	$ 46,000	$ 53,000	$ 1,198,000	$ 3,000	$ 2,325,000	679,000	$ 2,328,000	4,635,000	4,354,000	$ 1,930,000	3,579,000
Clinical materials revenue | Lilly
Collaborative Agreements disclosures
Costs of services and materials																$ 0		$ 0	$ 1,200,000		$ 1,100,000

Agreements - CytomX (Details)

Agreements - CytomX (Details) - USD ($)	3 Months Ended														6 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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Jan. 02, 2018	Jan. 31, 2014
Collaborative Agreements disclosures
Revenue from contract with customer	$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Deferred revenue	80,802,000																80,802,000				$ 89,967,000
CytomX
Collaborative Agreements disclosures
Deferred revenue											13,000,000									13,000,000
Potential milestone payments to be received																						$ 160,000,000
CytomX | Development milestones
Collaborative Agreements disclosures
Potential milestone payments to be received					7,000,000						10,000,000							7,000,000		10,000,000		10,000,000
CytomX | Phase 1 clinical trial
Collaborative Agreements disclosures
Potential milestone payments to be received	1,000,000																1,000,000
CytomX | Phase 2 clinical trial
Collaborative Agreements disclosures
Potential milestone payments to be received	3,000,000																3,000,000
CytomX | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payments to be received					23,000,000						50,000,000							23,000,000		50,000,000		50,000,000
CytomX | Milestone payments
Collaborative Agreements disclosures
Potential milestone payments to be received					50,000,000						100,000,000							50,000,000		100,000,000		$ 100,000,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer	1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
License and milestone fees | CytomX
Collaborative Agreements disclosures
Revenue from contract with customer																		12,700,000
Potential milestone payments to be received					80,000,000													80,000,000
License and milestone fees | CytomX | Phase 1 clinical trial
Collaborative Agreements disclosures
Revenue from contract with customer																		1,000,000
License and milestone fees | CytomX | Milestone payments
Collaborative Agreements disclosures
Potential milestone payments to be received											160,000,000									160,000,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer	218,000	388,000	388,000	383,000	452,000	650,000	902,000	1,478,000	1,427,000	1,354,000	1,335,000	1,059,000	848,000	772,000	2,781,000	1,620,000	1,377,000	3,482,000	5,175,000	4,014,000
Costs of services and materials															22,000
Research and development support | CytomX
Collaborative Agreements disclosures
Costs of services and materials															427,000		195,000	256,000		868,000
Clinical materials revenue
Collaborative Agreements disclosures
Revenue from contract with customer	$ 2,170,000	$ 1,427,000	$ 336,000	$ 702,000	$ 1,829,000	$ 1,248,000	$ 599,000	$ 678,000	$ 633,000	$ 46,000	$ 53,000	$ 1,198,000	$ 3,000	$ 2,325,000	679,000	$ 2,328,000	4,635,000	4,354,000	$ 1,930,000	3,579,000
Clinical materials revenue | CytomX
Collaborative Agreements disclosures
Costs of services and materials															$ 0		$ 3,500,000	$ 1,000,000		$ 0

Agreements - Takeda (Details)

Agreements - Takeda (Details)	1 Months Ended		3 Months Ended														6 Months Ended		12 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2015USD ($)item	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, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2018USD ($)item	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)	May 31, 2018USD ($)	Jan. 02, 2018USD ($)
Collaborative Agreements disclosures
Revenue from contract with customer			$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Takeda
Collaborative Agreements disclosures
Term of agreement		3 years
Number of single-target licenses | item																			1
Term of extension of the agreement		1 year
Potential milestone payment		$ 210,000,000
Estimated term of development and commercialization license		25 years
Costs of services and materials																	0					0
Takeda | Maximum
Collaborative Agreements disclosures
Number of single-target licenses | item		2
Takeda | Development milestones
Collaborative Agreements disclosures
Potential milestone payment		$ 30,000,000
Takeda | Phase 2 clinical trial
Collaborative Agreements disclosures
Potential milestone payment			10,000,000																$ 10,000,000
Takeda | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payment		85,000,000
Takeda | Milestone payments
Collaborative Agreements disclosures
Potential milestone payment		95,000,000
Takeda | Technological Improvements
Collaborative Agreements disclosures
Potential milestone payment																								$ 400,000
Takeda | Right-to-test agreement
Collaborative Agreements disclosures
Potential milestone payment		4,000,000
Takeda | Option to expand scope of right-to-test
Collaborative Agreements disclosures
Potential milestone payment		8,000,000
ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Revenue from contract with customer																			5,000,000
ASU 2014-09 | Adjustments due to new guidance | Takeda | Phase 1 clinical trial
Collaborative Agreements disclosures
Potential milestone payment							5,000,000													5,000,000			$ 5,000,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer			1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
License and milestone fees | Takeda
Collaborative Agreements disclosures
Revenue from contract with customer	$ 10,900,000																					8,600,000
Potential milestone payment		210,000,000
License and milestone fees | ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Potential milestone payment			5,000,000																5,000,000
Upfront payment | Takeda
Collaborative Agreements disclosures
Revenue from contract with customer		$ 20,000,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer			218,000	388,000	388,000	383,000	452,000	650,000	902,000	1,478,000	1,427,000	1,354,000	1,335,000	1,059,000	848,000	772,000	2,781,000	1,620,000	1,377,000	3,482,000	5,175,000	4,014,000
Costs of services and materials																	22,000
Research and development support | Takeda
Collaborative Agreements disclosures
Costs of services and materials																	678,000		199,000	913,000		469,000
Clinical materials revenue
Collaborative Agreements disclosures
Revenue from contract with customer			$ 2,170,000	$ 1,427,000	$ 336,000	$ 702,000	$ 1,829,000	$ 1,248,000	$ 599,000	$ 678,000	$ 633,000	$ 46,000	$ 53,000	$ 1,198,000	$ 3,000	$ 2,325,000	$ 679,000	$ 2,328,000	4,635,000	4,354,000	$ 1,930,000	$ 3,579,000
Clinical materials revenue | Takeda
Collaborative Agreements disclosures
Costs of services and materials																			$ 650,000,000,000	$ 2,100,000

Agreements - Fusion (Details)

Agreements - Fusion (Details) - USD ($)	3 Months Ended														6 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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016
Collaborative Agreements disclosures
Revenue from contract with customer	$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Fusion Pharmaceuticals
Collaborative Agreements disclosures
Potential milestone payment	500,000																500,000
Fusion Pharmaceuticals | Development milestones
Collaborative Agreements disclosures
Potential milestone payment									15,000,000						15,000,000				15,000,000
Fusion Pharmaceuticals | Phase 2 clinical trial
Collaborative Agreements disclosures
Potential milestone payment	1,500,000																1,500,000
Fusion Pharmaceuticals | Milestone payments
Collaborative Agreements disclosures
Potential milestone payment									35,000,000						35,000,000				35,000,000
ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Revenue from contract with customer																	5,000,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer	1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
License and milestone fees | Fusion Pharmaceuticals
Collaborative Agreements disclosures
Potential milestone payment									50,000,000						50,000,000				50,000,000
License and milestone fees | Fusion Pharmaceuticals | Phase 1 clinical trial
Collaborative Agreements disclosures
Revenue from contract with customer																	500,000
License and milestone fees | ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Potential milestone payment	5,000,000																5,000,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer	218,000	388,000	388,000	383,000	452,000	650,000	902,000	1,478,000	1,427,000	1,354,000	1,335,000	1,059,000	848,000	772,000	2,781,000	1,620,000	1,377,000	3,482,000	5,175,000	4,014,000
Clinical materials revenue
Collaborative Agreements disclosures
Revenue from contract with customer	$ 2,170,000	$ 1,427,000	$ 336,000	$ 702,000	$ 1,829,000	$ 1,248,000	$ 599,000	$ 678,000	$ 633,000	$ 46,000	$ 53,000	$ 1,198,000	$ 3,000	$ 2,325,000	$ 679,000	$ 2,328,000	$ 4,635,000	$ 4,354,000	$ 1,930,000	$ 3,579,000

Agreements - Debiopharm (Detail

Agreements - Debiopharm (Details) - USD ($)	1 Months Ended		3 Months Ended														6 Months Ended		12 Months Ended
	Dec. 31, 2017	May 31, 2017	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	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016
Collaborative Agreements disclosures
Revenue from contract with customer			$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer			1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer			218,000	$ 388,000	$ 388,000	$ 383,000	$ 452,000	$ 650,000	$ 902,000	$ 1,478,000	$ 1,427,000	$ 1,354,000	$ 1,335,000	$ 1,059,000	$ 848,000	$ 772,000	2,781,000	$ 1,620,000	1,377,000	3,482,000	$ 5,175,000	$ 4,014,000
Costs of services and materials																	$ 22,000
Debiopharm | Phase 3 Clinical Trial
Collaborative Agreements disclosures
Potential milestone payment			$ 25,000,000																25,000,000
Debiopharm | Transfer of ImmunoGen technologies
Collaborative Agreements disclosures
Revenue from contract with customer	$ 4,500,000
Potential milestone payment		$ 5,000,000
Debiopharm | Upfront payment | IMGN529 program
Collaborative Agreements disclosures
Revenue from contract with customer		$ 25,000,000
Debiopharm | License and milestone fees | IMGN529 program
Collaborative Agreements disclosures
Revenue from contract with customer																				$ 29,500,000
Debiopharm | License and milestone fees | Transfer of ImmunoGen technologies
Collaborative Agreements disclosures
Revenue from contract with customer																			500,000
Debiopharm | Research and development support
Collaborative Agreements disclosures
Costs of services and materials																			$ 99,000

Agreements - Jazz Pharmaceutica

Agreements - Jazz Pharmaceuticals (Details) - Jazz Pharmaceuticals $ in Millions	1 Months Ended	12 Months Ended
	Aug. 31, 2017USD ($)productitem	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Collaborative Agreements disclosures
Number of early stage ADC programs | item	2
Number of ADC programs | item	3
Number of products with rights to co-commercialize | product	1
Number of products with rights under certain limited circumstances | product	2
Potential milestone payment	$ 100
Term of agreement	7 years
Offset to research and development expense		$ 10	$ 3.3
Upfront payment
Collaborative Agreements disclosures
Deferred revenue	$ 75	$ 75

Property and Equipment (Details

Property and Equipment (Details) - USD ($)	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016	Jan. 02, 2018
Property and Equipment
Property and equipment, gross		$ 52,395,000	$ 71,982,000
Less accumulated depreciation		(39,504,000)	(57,444,000)
Property and equipment, net		12,891,000	14,538,000		$ 14,538,000
Depreciation expense	$ 3,074,000	7,411,000	5,963,000	$ 5,327,000
Leasehold improvements
Property and Equipment
Property and equipment, gross		20,684,000	36,460,000
Machinery and equipment
Property and Equipment
Property and equipment, gross		22,558,000	23,123,000
Computer hardware and software
Property and Equipment
Property and equipment, gross		5,494,000	8,273,000
Furniture and fixtures
Property and Equipment
Property and equipment, gross		3,546,000	3,710,000
Assets under construction
Property and Equipment
Property and equipment, gross		113,000	416,000
Equipment under capital leases
Property and Equipment
Less accumulated depreciation		(684,000)	(479,000)
Property and equipment, net	$ 449,000	$ 595,000	$ 449,000

Convertible 4.5% Senior Notes (

Convertible 4.5% Senior Notes (Details)	1 Months Ended	3 Months Ended										6 Months Ended		12 Months Ended
	Jun. 30, 2016USD ($)$ / shares	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, 2016USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)$ / shares
Convertible debt
Interest rate (as a percent)		4.50%												4.50%
Proceeds from issuance of debt																	$ 96,608,000
Issuance of debt transaction costs																	3,392,000
Interest expense		$ 25,000	$ 23,000	$ 23,000	$ 24,000	$ 28,000	$ 762,000	$ 1,125,000	$ 1,125,000	$ 1,099,000	$ 1,150,000		$ 2,249,000	$ 95,000	$ 3,040,000	$ 2,387,000	138,000
Convertible Notes
Convertible debt
Interest rate (as a percent)		4.50%				4.50%				4.50%		4.50%	4.50%	4.50%	4.50%	4.50%
Principal amount of debt		$ 2,100,000								$ 100,000,000			$ 100,000,000	$ 2,100,000		$ 100,000,000
Proceeds from issuance of debt																$ 96,600,000
Debt converted												$ 97,900,000			$ 96,900,000
Shares issued with debt conversion (in shares) | shares												26,160,187
Shares issued with debt conversion adjustment (in shares) | shares												2,784,870
Debt Conversion other amount															1,000,000
Debt conversion loss															22,900,000
Accrued interest forfeited															743,000
Charges to paid in capital															2,500,000
Transaction costs														1,700,000
Interest expense													$ 2,200,000	95,000	3,000,000		138,000
Principal amount of debt for conversion calculations	$ 1,000					$ 1,000						$ 1,000			$ 1,000		$ 1,000
Ratio issued upon conversion	238.7775
Initial conversion price (in dollars per share) | $ / shares	$ 4.19																$ 4.19
Deferred financing costs		$ 50,000												$ 50,000

Liability Related to Sale of _3

Liability Related to Sale of Future Royalties (Details) $ in Thousands	1 Months Ended	6 Months Ended	12 Months Ended				48 Months Ended
	Jan. 31, 2019USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2018USD ($)
Liability Related to Sale of Future Royalties
Non-cash royalty revenue related to the sale of future royalties		$ 12,894	$ 32,154	$ 28,142	$ 25,299
Kadcyla
Liability Related to Sale of Future Royalties
Percentage of royalty payments if applicable threshold is met						85.00%
OMERS | Kadcyla
Liability Related to Sale of Future Royalties
Percentage of royalty payments			100.00%
IRH | Kadcyla
Liability Related to Sale of Future Royalties
Percentage of royalty payments						100.00%
Percentage of royalty payments if applicable threshold is met						15.00%
Transaction costs for royalty agreements						$ 5,900
Change in liability related to sale of future royalties
Liability related to sale of future royalties, net - beginning balance	$ 148,225		$ 169,413
Proceeds from sale of future royalties - net						$ 200,000	$ 194,135
Royalty payments received and paid			(31,805)				(103,624)
Non-cash interest expense recognized			10,617				57,714
Liability related to sale of future royalties, net - ending balance			$ 148,225	$ 169,413			$ 148,225
Effective annual interest rate						7.20%
Current effective interest rate			5.7
IRH | Kadcyla | Maximum
Liability Related to Sale of Future Royalties
Royalties threshold						$ 260,000
IRH | Kadcyla | Minimum
Liability Related to Sale of Future Royalties
Royalties threshold						$ 235,000
OMERS | Kadcyla | Subsequent event
Liability Related to Sale of Future Royalties
Non-cash royalty revenue related to the sale of future royalties	$ 65,200

Income Taxes - Expense (Details

Income Taxes - Expense (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Reconciliation of the expected statutory tax benefit to the actual income taxes
U.S. federal corporate tax rate (as a percent)	34.00%	21.00%	34.00%	34.00%
Loss before income tax expense	$ (78,883)	$ (168,843)	$ (96,012)	$ (144,817)
Expected tax benefit at 21%, 34%, 34% and 34%, respectively	(26,820)	(35,457)	(32,644)	(49,238)
Permanent differences	15	(103)	25	345
Incentive stock options	1,313	1,144	1,528	2,501
State tax benefit net of federal benefit	(4,157)	(10,622)	(3,537)	(7,954)
Change in valuation allowance, net	32,922	53,706	(63,238)	62,505
Federal research credit	(1,232)	(2,466)	(2,204)	(4,109)
Federal orphan drug credit	(2,901)	(6,934)	(7,118)	(4,241)
Expired loss and credit carryforwards				184
Change in U.S. tax law			97,479
Debt inducement			8,044
Lease incentive		109
Stock option expirations	860	623	1,665	7
Benefit for income taxes

Income Taxes - Carryforward (De

Income Taxes - Carryforward (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Federal
Carryforward
Operating loss carryforward	$ 665.6
NOL carryforwards, indefinitely	194
Credit carryforwards	59.4
State
Carryforward
Operating loss carryforward	501.1
Credit carryforwards	$ 13

Income Taxes - Deferred (Detail

Income Taxes - Deferred (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Deferred tax assets:
Net operating loss carryforwards		$ 171,437	$ 118,672
Research and development tax credit carryforwards		69,710	58,606
Property and other intangible assets		297	2,272
Deferred revenue		22,075	25,997
Stock-based compensation		12,849	12,125
Deferred lease incentive		2,639	2,889
Other liabilities		2,920	3,037
Royalty sale		38,593	47,143
Total deferred tax assets		320,520	270,741
Deferred tax liabilities:
Stock-based compensation		(156)
Royalty sale transaction costs		(625)	(859)
Total deferred tax liabilities		781	859
Valuation allowance		(319,739)	(269,882)
Net deferred tax assets/(liabilities)
Tax Cuts and Jobs Act (TCJA)
U.S. federal corporate tax rate (as a percent)	34.00%	21.00%	34.00%	34.00%
Resulting provision from revaluation of deferred tax assets and deferred tax liabilities as of TCJA enactment date		$ 97,500
Maximum
Tax Cuts and Jobs Act (TCJA)
U.S. federal corporate tax rate (as a percent)		35.00%

Capital Stock (Details)

Capital Stock (Details) - USD ($)	Mar. 28, 2018	Mar. 27, 2018	Jun. 30, 2018	Feb. 28, 2018	Jan. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2001
Stock-based compensation disclosure
Compensation expense						$ 8,100,000	$ 16,400,000	$ 11,100,000	$ 21,900,000
Aggregate number of common shares reserved for future issuance							24,700,000
Proceeds from issuance of common stock under stock plans							$ 4,301,000	$ 650,000	$ 5,161,000
Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares)						3,536,000	5,513,000	1,589,000	3,340,000
Options exercised (in shares)							742,000	191,000	555,000
Exercise price (in dollars per share)							$ 1.84
Exercise price (in dollars per share)							$ 12.21
Proceeds from issuance of common stock under stock plans							$ 3,500,000
Exercisable at the end of the period (in shares)						7,898,000	8,405,000	7,996,000	6,453,000
Weighted-Average Exercise Price (in dollars per share)						$ 13.15	$ 11.47	$ 12.16	$ 12.63
Deferred share units
Stock-based compensation disclosure
Compensation expense						$ 215,000	$ 361,000	$ 206,000	$ 380,000
2001 Non-Employee Director Stock Plan
Stock-based compensation disclosure
Aggregate number of common shares reserved for future issuance											50,000
2001 Non-Employee Director Stock Plan | Retiring director
Stock-based compensation disclosure
Compensation expense			$ 72,000
2001 Non-Employee Director Stock Plan | Deferred share units
Stock-based compensation disclosure
Compensation expense						$ (7,000)	$ 31,000	$ 28,000	$ (72,000)
Stock units outstanding (in shares)							6,000
2018 Plan | Stock options
Stock-based compensation disclosure
Options exercised (in shares)							742,000
Compensation Policy for Non-Employee Directors | Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares)						40,000	128,000	80,000	80,000	80,000
Compensation Policy for Non-Employee Directors | Deferred share units
Stock-based compensation disclosure
Compensation expense						$ 215,000	$ 361,000	$ 206,000	$ 380,000
Common stock issued to retiring directors (in shares)			95,497	77,012	53,248	37,000	46,000	47,000	41,000
Common stock issued when a director ceases to be a member (in shares)							1
Stock units previously granted (in shares)						12,000	10,500	12,000	12,000
Non-employee directors-initial grant | Deferred share units
Stock-based compensation disclosure
Vesting period							3 years
Stock options granted to directors (in shares)							6,500
Non-employee directors-after year one | Deferred share units
Stock-based compensation disclosure
Vesting period							1 year
Stock options granted to directors (in shares)							4,000
Annual stock option awards | Stock options
Stock-based compensation disclosure
Vesting period							1 year
Stock options granted to directors (in shares)	18,000	10,000
Off-Cycle initial awards | Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares)	18,000	10,000

Restructuring Charge (Details)

Restructuring Charge (Details)	1 Months Ended	3 Months Ended								6 Months Ended	9 Months Ended			12 Months Ended
	Sep. 30, 2016USD ($)ft²item	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)ft²	Sep. 30, 2016USD ($)ft²	Dec. 31, 2016USD ($)ft²shares	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2016USD ($)ft²	Dec. 31, 2018USD ($)employeeshares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)ft²	Jun. 30, 2016USD ($)shares
Restructuring
Stock compensation expense (reduction)										$ 8,100,000				$ 16,400,000	$ 11,100,000		$ 21,900,000
Leasehold impairment charge										970,000					180,000
Restructuring Reserve
Initial charge related to employee benefits, Beginning Balance				$ 1,189,000							$ 1,189,000
Additional charges during the year		$ 406,000	$ 870,000	$ 686,000	$ 1,731,000	$ 393,000	$ 386,000	$ 301,000	$ 4,130,000	4,431,000	2,347,000			3,693,000	779,000	$ 4,431,000
Payments during the period											(2,695,000)
Balance at the End of the year		$ 841,000			1,189,000						$ 841,000			$ 841,000
Workforce reduction
Restructuring
Approximate positions to be eliminated (as a percent)	17.00%
Approximate positions to be eliminated	65													22
Approximate current positions to be eliminated | item	60
One-time charge for severance					1,200,000					2,800,000
Benefit plan severance cost										593,000		$ 2,300,000
Restructuring Reserve
Additional charges during the year										$ 4,400,000
930 Winter Street, Walham, MA
Restructuring
Area of space leased | ft²								10,281		10,281						10,281
930 Winter Street, Walham, MA | Lease
Restructuring
Area of space leased | ft²	10,281								10,281				10,281
Estimated period to sub-lease													9 months
Leasehold impairment charge													$ 970,000		$ 779,000
Leasehold improvement cost	$ 193,000								$ 193,000				$ 193,000
Stock options
Restructuring
Forfeited (in shares) | shares										1,670,000				1,178,000	3,106,000		661,000
Granted (in shares) | shares										3,536,000				5,513,000	1,589,000		3,340,000
Stock options | Workforce reduction
Restructuring
Forfeited (in shares) | shares										762,000
Stock compensation expense (reduction)					$ 157,000					$ (837,000)

Commitments and Contingencies_2

Commitments and Contingencies (Details) € in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2016USD ($)ft²	Dec. 31, 2018USD ($)item	Dec. 31, 2017USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2018EUR (€)ft²	Dec. 31, 2018USD ($)ft²	Apr. 30, 2018USD ($)ft²	Jan. 02, 2018USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2013ft²
Operating leases
Construction allowance			$ 5,129,000			$ 4,675,000		$ 5,129,000	$ 2,000,000
Facilities rent expense, net of sublease income	$ 3,500,000	$ 7,700,000	$ 6,800,000	$ 6,500,000
Minimum rental commitments under the non-cancelable operating lease agreements
2,019						5,498,000
2,020						5,419,000
2,021						5,257,000
2,022						5,323,000
2,023						5,450,000
Thereafter						12,336,000
Total minimum lease payments						39,283,000
Operating costs and real estate taxes per year		$ 3,000,000
Obligations under capital leases						0
Collaborations and Licenses
Potential milestone payable						80,000,000
Manufacturing commitments
Collaborations and Licenses
Manufacturing commitment						$ 1,300,000
Noncancelable commitment | €					€ 22
830 Winter Street, Waltham, MA
Operating leases
Area of space leased | ft²					120,000	120,000	10,000
Number of additional terms for which lease agreement can be extended | item		2
Operating lease term extension period					5 years	5 years
Construction allowance							$ 400,000
930 Winter Street, Walham, MA
Operating leases
Area of space leased | ft²	10,281
Construction allowance	$ 617,000
333 Providence Hwy, Norwood MA
Operating leases
Area of space leased | ft²					43,850	43,850
100 River Ridge Drive, Norwood, MA
Operating leases
Area of space leased | ft²										7,507
Operating lease term period										5 years 2 months

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($)	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Employee Benefit Plans
Maximum employees' contribution (as a percent)		100.00%
Matching contribution of first 6% of eligible employees' contributions (as a percent)		50.00%
Percentage of eligible employees' contributions matched by the company		6.00%
Company's contribution	$ 536,000	$ 1,000,000	$ 982,000	$ 1,100,000

Quarterly Financial Informati_3

Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended														6 Months Ended		9 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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016
Revenues:
Total revenues	$ 13,416	$ 10,928	$ 9,287	$ 19,815	$ 39,448	$ 8,480	$ 39,020	$ 28,499	$ 13,846	$ 7,660	$ 7,408	$ 19,714	$ 18,029	$ 14,851	$ 21,506	$ 32,880		$ 53,446	$ 115,447	$ 48,628	$ 60,002
Expenses:
Research and development	43,681	47,243	38,701	44,831	39,843	31,689	35,319	32,888	33,657	32,909	38,652	36,094	38,199	35,132	66,566	73,331		174,456	139,739	141,312	148,077
General and administrative	9,752	8,347	8,652	9,995	9,048	7,908	8,836	8,119	8,536	9,459	9,298	11,235	8,054	8,329	17,995	16,383		36,746	33,911	38,528	36,916
Restructuring charge	406	870	686	1,731	393			386	301	4,130					4,431		$ 2,347	3,693	779	4,431
Total operating expenses	53,839	56,460	48,039	56,557	49,284	39,597	44,155	41,393	42,494	46,498	47,950	47,329	46,253	43,461	88,992	89,714		214,895	174,429	184,271	184,993
Loss from operations	(40,423)	(45,532)	(38,752)	(36,742)	(9,836)	(31,117)	(5,135)	(12,894)	(28,648)	(38,838)	(40,542)	(27,615)	(28,224)	(28,610)	(67,486)	(56,834)		(161,449)	(58,982)	(135,643)	(124,991)
Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes	(2,428)	(2,546)	(2,611)	(3,046)	(3,221)	(3,385)	(3,501)	(3,575)	(3,647)	(5,018)	(4,956)	(4,972)	(5,059)	(5,143)	(8,665)	(10,202)		(10,631)	(13,682)	(18,593)	(20,130)
Interest expense on convertible senior notes	(25)	(23)	(23)	(24)	(28)	(762)	(1,125)	(1,125)	(1,099)	(1,150)					(2,249)			(95)	(3,040)	(2,387)	(138)
Other (expense) income, net	1,077	1,294	(238)	1,199	691	773	894	249	(758)	275	(424)	659	56	13
Non-cash debt conversion expense					(724)	(22,191)													(22,915)
Net loss	$ (41,799)	$ (46,807)	$ (41,624)	$ (38,613)	$ (13,118)	$ (56,682)	$ (8,867)	$ (17,345)	$ (34,152)	$ (44,731)	$ (45,922)	$ (31,928)	$ (33,227)	$ (33,740)	$ (78,883)	$ (66,967)		$ (168,843)	$ (96,012)	$ (156,733)	$ (144,817)
Basic and diluted net loss per common share (in dollars per share)	$ (0.28)	$ (0.32)	$ (0.31)	$ (0.30)	$ (0.11)	$ (0.61)	$ (0.10)	$ (0.20)	$ (0.39)	$ (0.51)	$ (0.53)	$ (0.37)	$ (0.38)	$ (0.39)	$ (0.91)	$ (0.77)		$ (1.21)	$ (0.98)	$ (1.80)	$ (1.67)
License and milestone fees
Revenues:
Total revenues	$ 1,747	$ 672	$ 1,321	$ 11,540	$ 29,580	$ 79	$ 31,080	$ 18,730	$ 5,076	$ 76	$ 76	$ 10,077	$ 10,692	$ 6,070	$ 5,152	$ 16,762		$ 15,280	$ 79,469	$ 15,305	$ 26,915
Royalty revenue
Revenues:
Total revenues													195			195					195
Non-cash royalty revenue related to the sale of future royalties
Revenues:
Total revenues	9,281	8,441	7,242	7,190	7,587	6,503	6,439	7,613	6,710	6,184	5,944	7,380	6,291	5,684	12,894	11,975		32,154	28,142	26,218	25,299
Research and development support
Revenues:
Total revenues	218	388	388	383	452	650	902	1,478	1,427	1,354	1,335	1,059	848	772	2,781	1,620		1,377	3,482	5,175	4,014
Clinical materials revenue
Revenues:
Total revenues	$ 2,170	$ 1,427	$ 336	$ 702	$ 1,829	$ 1,248	$ 599	$ 678	$ 633	$ 46	$ 53	$ 1,198	$ 3	$ 2,325	$ 679	$ 2,328		$ 4,635	$ 4,354	$ 1,930	$ 3,579

Stub Period Comparative Data _3

Stub Period Comparative Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended														6 Months Ended		9 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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016
Revenues:
Total revenues	$ 13,416	$ 10,928	$ 9,287	$ 19,815	$ 39,448	$ 8,480	$ 39,020	$ 28,499	$ 13,846	$ 7,660	$ 7,408	$ 19,714	$ 18,029	$ 14,851	$ 21,506	$ 32,880		$ 53,446	$ 115,447	$ 48,628	$ 60,002
Operating Expenses:
Research and development	43,681	47,243	38,701	44,831	39,843	31,689	35,319	32,888	33,657	32,909	38,652	36,094	38,199	35,132	66,566	73,331		174,456	139,739	141,312	148,077
General and administrative	9,752	8,347	8,652	9,995	9,048	7,908	8,836	8,119	8,536	9,459	9,298	11,235	8,054	8,329	17,995	16,383		36,746	33,911	38,528	36,916
Restructuring charge	406	870	686	1,731	393			386	301	4,130					4,431		$ 2,347	3,693	779	4,431
Total operating expenses	53,839	56,460	48,039	56,557	49,284	39,597	44,155	41,393	42,494	46,498	47,950	47,329	46,253	43,461	88,992	89,714		214,895	174,429	184,271	184,993
Loss from operations	(40,423)	(45,532)	(38,752)	(36,742)	(9,836)	(31,117)	(5,135)	(12,894)	(28,648)	(38,838)	(40,542)	(27,615)	(28,224)	(28,610)	(67,486)	(56,834)		(161,449)	(58,982)	(135,643)	(124,991)
Investment income, net															259	111		4,227	1,146	473	325
Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes	(2,428)	(2,546)	(2,611)	(3,046)	(3,221)	(3,385)	(3,501)	(3,575)	(3,647)	(5,018)	(4,956)	(4,972)	(5,059)	(5,143)	(8,665)	(10,202)		(10,631)	(13,682)	(18,593)	(20,130)
Interest expense on convertible senior notes	(25)	(23)	(23)	(24)	(28)	(762)	(1,125)	(1,125)	(1,099)	(1,150)					(2,249)			(95)	(3,040)	(2,387)	(138)
Other income (expense), net															(742)	(42)		(895)	1,461	(583)	117
Net loss	$ (41,799)	$ (46,807)	$ (41,624)	$ (38,613)	$ (13,118)	$ (56,682)	$ (8,867)	$ (17,345)	$ (34,152)	$ (44,731)	$ (45,922)	$ (31,928)	$ (33,227)	$ (33,740)	$ (78,883)	$ (66,967)		$ (168,843)	$ (96,012)	$ (156,733)	$ (144,817)
Basic and diluted net loss per common share (in dollars per share)	$ (0.28)	$ (0.32)	$ (0.31)	$ (0.30)	$ (0.11)	$ (0.61)	$ (0.10)	$ (0.20)	$ (0.39)	$ (0.51)	$ (0.53)	$ (0.37)	$ (0.38)	$ (0.39)	$ (0.91)	$ (0.77)		$ (1.21)	$ (0.98)	$ (1.80)	$ (1.67)
License and milestone fees
Revenues:
Total revenues	$ 1,747	$ 672	$ 1,321	$ 11,540	$ 29,580	$ 79	$ 31,080	$ 18,730	$ 5,076	$ 76	$ 76	$ 10,077	$ 10,692	$ 6,070	$ 5,152	$ 16,762		$ 15,280	$ 79,469	$ 15,305	$ 26,915
Royalty revenue
Revenues:
Total revenues													195			195					195
Non-cash royalty revenue related to the sale of future royalties
Revenues:
Total revenues	9,281	8,441	7,242	7,190	7,587	6,503	6,439	7,613	6,710	6,184	5,944	7,380	6,291	5,684	12,894	11,975		32,154	28,142	26,218	25,299
Research and development support
Revenues:
Total revenues	218	388	388	383	452	650	902	1,478	1,427	1,354	1,335	1,059	848	772	2,781	1,620		1,377	3,482	5,175	4,014
Clinical materials revenue
Revenues:
Total revenues	$ 2,170	$ 1,427	$ 336	$ 702	$ 1,829	$ 1,248	$ 599	$ 678	$ 633	$ 46	$ 53	$ 1,198	$ 3	$ 2,325	$ 679	$ 2,328		$ 4,635	$ 4,354	$ 1,930	$ 3,579