Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 37,070	$ 45,488
Research and development credit carryforwards	3,690	3,355
Accruals and other	2,263	2,079
Capitalized license and organization costs	0	61
Capitalized start-up costs	150	246
Other	38	0
Total gross deferred tax asset	43,211	51,229
Deferred tax liabilities:
IPR&D	(12,528)	(16,335)
Property and equipment	(107)	(189)
Total gross deferred tax liabilities	(12,635)	(16,524)
Valuation allowance	(43,104)	(51,040)
Net deferred tax liability	$ (12,528)	$ (16,335)