Income Taxes - Deferred Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Valuation allowance	$ 163,040	$ 122,441	$ 95,800
Effect Of Tax Cuts And Jobs Act Of 2017 [Abstract]
Corporate tax rate	21.00%	21.00%	34.00%
Deferred tax assets
Net operating loss carryforwards	$ 124,777	$ 95,321
Research and development tax credit carryforwards	18,189	15,632
Reserves and accruals	10,002	7,839
Lease Liabilities	7,838
Deferred revenue	3,288	83
Stock based compensation	6,106	4,076
Total deferred tax assets before valuation allowance	170,200	122,951
Less: valuation allowance	(163,040)	(122,441)	$ (95,800)
Deferred tax assets, net	7,160	510
Deferred tax liabilities
Property and equipment		(510)
Right-of-use lease assets	(7,160)
Net deferred tax assets