Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Federal and State net operating loss carryforward	$ 293,736	$ 270,177
Foreign net operating loss carryforward	13,520	12,321
Research tax credits	37,066	33,633
Non-cash stock-based compensation	13,679	10,888
Original discount interest	4,326	5,687
Other	5,957	7,987
Total deferred tax assets	368,284	340,693
Valuation allowance	(365,772)	(337,515)
Net deferred tax assets	2,512	3,178
Intangibles	(1,279)	(1,492)
Other	(1,233)	(1,686)
Total deferred tax liabilities	$ (2,512)	$ (3,178)