Income Taxes - Deferred Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 22, 2017	Dec. 31, 2016
Gross Deferred Tax Assets
Net Operating Loss Carryforwards		$ 146,228		$ 174,555
Foreign Net Operating Loss Carryforwards		3,572		1,124
Tax Credit Carryforwards		36,458		32,306
Deferred Research and Development Expenses		79,272		109,520
Stock-based Compensation		10,718		12,362
Fixed Assets		1,305		1,526
Deferred Revenue		686		1,418
Accrued Expenses and Other		316		894
Gross Deferred Tax Assets		278,555		333,705
Gross Deferred Tax Liabilities
Other Acquired Intangibles		(1,792)		(2,868)
IPR&D Intangibles		(15,992)		(28,054)
Total Deferred Tax Assets and Liabilities		260,771		302,783
Valuation Allowance		(264,543)		(330,837)
Net Deferred Tax Liability		(3,772)		$ (28,054)
Principal components of the deferred tax assets and liabilities
Increase in deferred tax and valuation allowance		$ 17,700
U.S. federal corporate income tax rate (as a percent)		35.00%
Change in tax rate, deferred tax liability benefit		$ 6,900
Additional income tax benefit leading to tax liabilities		12,200
Revaluation of deferred tax asset		99,500
Income tax benefit		$ 5,200
Forecast
Principal components of the deferred tax assets and liabilities
U.S. federal corporate income tax rate (as a percent)	21.00%
Maximum
Principal components of the deferred tax assets and liabilities
U.S. federal corporate income tax net operating losses (as a percent)			80.00%