Income Taxes - Deferred Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Valuation allowance	$ 222,521	$ 163,040
Effect Of Tax Cuts And Jobs Act Of 2017 [Abstract]
Corporate tax rate	21.00%	21.00%	21.00%
Deferred tax assets
Net operating loss carryforwards	$ 177,899	$ 124,777
Research and development tax credit carryforwards	24,332	18,189
Reserves and accruals	21,770	10,002
Lease Liabilities	7,123	7,838
Deferred revenue	6,386	3,288
Stock based compensation	10,673	6,106
Total deferred tax assets before valuation allowance	248,183	170,200
Less: valuation allowance	(222,521)	(163,040)
Deferred tax assets, net	25,662	7,160
Deferred tax liabilities
Convertible debt	(19,143)
Right-of-use lease assets	(6,519)	(7,160)
Net deferred tax assets