Income Taxes - Summary of Reconciliation of Company's Effective Tax Rate to Federal Statutory Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Tax at federal statutory rate	$ (32,464)	$ (14,020)	$ (25,076)
State income tax, net of federal tax benefit	(6,764)	(3,898)	(2,255)
Foreign tax rate differential	626	(493)	2,805
Stock-based compensation	2,378	2,645	1,981
Transition tax	0	2,261	0
Revaluation of deferred tax assets and liabilities	0	(10,259)	0
Research and development credits	(5,247)	(4,028)	(992)
Intangible asset write-off	0	0	2,434
Other	(106)	659	2,092
Change in valuation allowance	41,725	11,086	23,715
Total provision for (benefit from) income taxes	$ 148	$ (16,047)	$ 4,704