Notes Payable, net - Schedule of debt outstanding, net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Principal Amount Due	$ 0	$ 63,341
Less: Unamortized debt issuance costs and discounts	0	(11,407)
Notes payable, net	0	51,934
2019 Loan and Security Agreement
Debt Instrument [Line Items]
Principal Amount Due	0	25,000
Subordinated Note Purchase and Security Agreement
Debt Instrument [Line Items]
Principal Amount Due	0	32,461
Notes payable, net		32,500
Paycheck Protection Program Loan
Debt Instrument [Line Items]
Principal Amount Due	$ 0	$ 5,880