Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Employee and non-employee stock options
Stock based compensation expense
Options granted (in shares)	150,000
Stock-based compensation expense	$ 23,232	$ 7,417
Unrecognized compensation expense	$ 215,400
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	$ 708	314
Employee and non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	3,874	1,842
Employee and non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	18,650	5,261
Employee stock options
Stock based compensation expense
Stock-based compensation expense	22,962	7,248
Employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense	708	314
Employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	3,650	1,682
Employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 18,604	5,252
Non-employee stock options
Stock based compensation expense
Options granted (in shares)	34,376
Options unvested (in shares)	2,917
Stock-based compensation expense	$ 270	169
Non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	224	160
Non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 46	$ 9