Income Taxes - Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax liabilities:
Intangible assets	$ 0	$ 1,764
Convertible notes	4,263	0
Total deferred tax liabilities	4,263	1,764
Deferred tax assets:
Loss carryforwards	85,263	77,194
Intangible assets	117	0
Capital loss carryforward	852	840
Property and equipment	1,067	1,096
License fees	7,776	8,351
Accrued expenses and other	549	886
Stock-based compensation	4,059	3,445
Credits	418	0
Total deferred tax assets before valuation allowance	100,101	91,812
Less: valuation allowance	(95,838)	(90,048)
Total deferred tax assets	4,263	1,764
Net deferred tax assets	$ 0	$ 0