Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee and non-employee stock options
Stock based compensation expense
Options granted (in shares)			391,000
Stock-based compensation expense	$ 26,459	$ 15,032	$ 84,797	$ 34,406
Unrecognized compensation expense	195,300		$ 195,300
Unrecognized compensation expense, weighted average period of recognition			2 years 9 months 18 days
Employee and non-employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense	1,262	458	$ 3,246	1,213
Employee and non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	6,652	3,098	17,142	7,853
Employee and non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	18,544	11,476	64,409	25,340
Employee stock options
Stock based compensation expense
Stock-based compensation expense	25,982	14,943	83,645	33,790
Employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense	1,262	458	3,246	1,213
Employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	6,242	3,081	16,168	7,394
Employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 18,478	11,404	$ 64,231	25,183
Non-employee stock options
Stock based compensation expense
Options granted (in shares)			32,053
Options unvested (in shares)	1,459		1,459
Stock-based compensation expense	$ 477	89	$ 1,152	616
Non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	410	17	974	459
Non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 67	$ 72	$ 178	$ 157