Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee and non-employee stock options
Stock based compensation expense
Options granted (in shares)			457,000
Stock-based compensation expense	$ 15,032	$ 10,247	$ 34,406	$ 20,102
Unrecognized compensation expense	89,200		$ 89,200
Unrecognized compensation expense, weighted average period of recognition			2 years 8 months 12 days
Employee and non-employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense	458	269	$ 1,213	662
Employee and non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	3,098	1,580	7,853	3,738
Employee and non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	11,476	8,398	25,340	15,702
Employee stock options
Stock based compensation expense
Stock-based compensation expense	14,943	10,150	33,790	19,563
Employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense	458	258	1,213	641
Employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	3,081	1,580	7,394	3,738
Employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 11,404	8,312	$ 25,183	15,184
Non-employee stock options
Stock based compensation expense
Options granted (in shares)			51,737
Options unvested (in shares)	7,814		7,814
Stock-based compensation expense	$ 89	97	$ 616	539
Non-employee stock options | Cost of revenues
Stock based compensation expense
Stock-based compensation expense		11		21
Non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	17		459
Non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 72	$ 86	$ 157	$ 518