Income Taxes - Reconciliation of the Income Tax Benefit at the U.S. Federal Statutory Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax provision at the federal statutory rate	$ 16,936	$ 11,566	$ 11,308
State and local income taxes net of federal benefit	973	3,839	(691)
Foreign income tax rate differential	(5,454)	(298)	(11,878)
Stock-based compensation	(16,281)	(11,717)	(12,584)
Research and development credit	(9,864)	(4,115)	(1,098)
U.S. tax reform	(4,197)	3,897	(31,063)
Non-deductible expenses	1,784	(329)	168
Uncertain tax positions	380	382	789
Change in valuation allowance	0	(28,733)	(4,673)
Return to provision adjustment	500	3,293	167
Other	(25)	(198)	20
Total income tax benefit	$ (15,248)	$ (22,413)	$ (49,535)