Income Taxes - Effective Income Tax Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory rate									21.00%	21.00%	35.00%
Tax benefit at federal statutory rate									$ (10,079)	$ (10,463)	$ (15,528)
State taxes, net of federal benefit									(5,015)	(2,587)	(1,802)
Revaluation of deferred tax items due to tax rate change (federal and state)									0	0	22,880
Revaluation of deferred tax asset for current year net operating loss due to tax rate change									0	0	4,134
Section 162(m) limitations									2,944	1,625	37
Stock-based compensation									(14,728)	(2,327)	(559)
Permanent differences including gain on foreign restructuring, and meals & entertainment									1,103	2,815	5,663
Tax benefit of federal R&D credit									(3,141)	(3,289)	(2,366)
Recognition of excess tax benefits related to share-based payments									0	0	(3,606)
Valuation allowance									29,236	14,044	(8,586)
Other									(181)	429	(206)
Total income tax provision	$ 38	$ 98	$ (8)	$ 11	$ 204	$ 17	$ 21	$ 5	$ 139	$ 247	$ 61