Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating losses	$ 53,901	$ 72,588
Credits	6,221	5,016
Deferred revenues	3,334	1,025
Stock-based compensation	2,872	3,750
Reserves and accruals	2,028	2,952
Depreciation	1,573	2,516
Intangible assets	3,172	5,536
Capital losses	576	933
Unrealized gain/loss	295	277
Other assets	78	110
Total deferred tax assets:	74,050	94,703
Deferred tax liabilities:
Other	(115)	(103)
Total deferred tax liabilities:	(115)	(103)
Valuation allowance	(74,010)	(94,663)
Net deferred tax liabilities	$ (75)	$ (63)