Income Taxes - Summary of Significant Components of Company's Net Deferred Income Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net deferred tax assets:
Net operating loss carryforwards	$ 142,991	$ 112,375
Stock-based compensation	22,785	17,734
U.S. tax credit carryforwards	10,980	5,996
Envisia asset acquisition	5,476	5,888
Basis difference in intangibles	7,625	0
Convertible Notes	(22,822)	0
Other assets	5,154	2,857
Other liabilities	(1,867)	(1,535)
Valuation allowance	(170,322)	(143,315)	$ (83,400)	$ (56,700)
Total net deferred income taxes	$ 0	$ 0