Income Taxes - Summary of Significant Components of Company's Net Deferred Income Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net deferred tax assets:
Net operating loss carryforwards	$ 169,070	$ 142,991
Stock-based compensation	29,884	22,785
U.S. tax credit carryforwards	13,526	10,980
Envisia asset acquisition	5,007	5,476
Basis difference in intangibles	7,625	7,625
Convertible Notes	(19,028)	(22,822)
Other assets	10,697	8,996
Other liabilities	(5,416)	(5,709)
Valuation allowance	(211,365)	(170,322)	$ (143,300)	$ (83,400)
Total net deferred income taxes	$ 0	$ 0