Income Taxes - Deferred Tax Assets/Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 191,744	$ 171,437
Research and development tax credit carryforwards	75,084	69,710
Property and other intangible assets	809	297
Deferred revenue	36,008	22,075
Stock-based compensation	9,630	12,849
Operating Lease Liability	6,767	2,639
Other liabilities	2,255	2,920
Royalty sale	30,030	38,593
Total deferred tax assets	352,327	320,520
Deferred tax liabilities:
Stock-based compensation	(110)	(156)
Operating lease right of use asset	(4,258)
Royalty sale transaction costs	(408)	(625)
Total deferred tax liabilities	4,776	781
Valuation allowance	$ (347,551)	$ (319,739)