Stockholders' Equity - Changes in Stockholders' equity (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Increase (Decrease) in Stockholders' Equity
Period Start Balance	$ 124,060	$ 236,369
Balance (in shares)	11,957,635
Shares Issued under Stock Option and Employee Stock Purchase Plans	$ 9	374
Shares Issued in Connection with Cantor Agreement	4,151	11,689
Shares Issued in Connection with Kolltan Severance		38
Share-Based Compensation	1,693	2,488
Unrealized Gain (Loss) on Marketable Securities	19	(5)
Net Loss	(17,239)	(118,132)
Period End Balance	$ 112,693	134,082
Balance (in shares)	12,844,711
ASC 606
Increase (Decrease) in Stockholders' Equity
Adoption of ASC		1,261
Common Stock
Increase (Decrease) in Stockholders' Equity
Period Start Balance	$ 12	$ 9
Balance (in shares)	11,957,635	9,234,693
Shares Issued under Stock Option and Employee Stock Purchase Plans (in shares)	3,507	9,453
Shares Issued in Connection with Cantor Agreement	$ 1
Shares Issued in Connection with Cantor Agreement (in shares)	883,569	312,802
Shares Issued in Connection with Kolltan Severance (in shares)		971
Period End Balance	$ 13	$ 9
Balance (in shares)	12,844,711	9,557,919
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity
Period Start Balance	$ 1,083,903	$ 1,046,313
Shares Issued under Stock Option and Employee Stock Purchase Plans	9	374
Shares Issued in Connection with Cantor Agreement	4,150	11,689
Shares Issued in Connection with Kolltan Severance		38
Share-Based Compensation	1,693	2,488
Period End Balance	1,089,755	1,060,902
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity
Period Start Balance	2,583	2,564
Unrealized Gain (Loss) on Marketable Securities	19	(5)
Period End Balance	2,602	2,559
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Period Start Balance	(962,438)	(812,517)
Net Loss	(17,239)	(118,132)
Period End Balance	$ (979,677)	(929,388)
Accumulated Deficit \| ASC 606
Increase (Decrease) in Stockholders' Equity
Adoption of ASC		$ 1,261

Represents the number of shares issued to certain officers in lieu of cash payments

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Amount of increase to additional paid-in capital (APIC) from recognition of equity-based compensation.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Amount of the cumulative effect on retained earnings net of related income tax effect.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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