Income Taxes - Schedule of Components of Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred income tax assets:
Net operating loss carryforwards	$ 99,551	$ 95,342
Stock-based compensation	11,854	25,278
Accrued expenses	1,878	3,338
Research and development tax credits	568	543
Other	271	371
Gross deferred tax assets	114,122	124,872
Valuation allowance	(107,046)	(115,689)	$ (84,167)	$ (64,449)
Net deferred tax assets	7,076	9,183
Deferred tax liabilities:
Property, equipment and software	(3,540)	(5,424)
Intangible assets and goodwill	(4,348)	(6,753)
Gross deferred tax liabilities	(7,888)	(12,177)
Total net deferred tax liabilities	$ (812)	$ (2,994)