Provision for Income Taxes - Significant Components of Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
NOL and credit carryforwards	$ 29,034	$ 24,180
Deferred revenue	9,910	5,765
Accrued expenses and other	9,829	6,326
Stock-based compensation	4,598	2,743
Total deferred tax assets	53,371	39,014
Deferred tax liabilities:
Deferred expenses	(8,337)	(6,335)
Depreciation and amortization	(2,887)	(3,297)
Total deferred tax liabilities	(11,224)	(9,632)
Deferred tax assets less tax liabilities	42,147	29,382
Less: valuation allowance	(42,401)	(29,355)
Net deferred tax (liability) asset		$ 27
Net deferred tax (liability) asset	$ (254)