Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 56,612	$ 35,023
Tax credit carryforwards	19,133	9,565
Contract liabilities	13,516	0
Operating lease liability	15,686	0
Stock-based compensation	9,513	3,305
Accruals and other	11,815	17,181
Gross deferred tax assets	126,275	65,074
Valuation allowance	(112,713)	(60,915)
Net deferred tax assets	13,562	4,159
Deferred tax liabilities:
Property and equipment	(6,225)	(4,159)
Operating lease right-of-use asset	(7,337)	0
Net deferred tax assets	$ 0	$ 0