Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Jan. 01, 2020	Jul. 31, 2013
Guarantor Obligations
Total minimum payments		$ 5,141		$ 5,141		$ 6,716
Operating lease right-of-use assets, net		3,667		3,667		4,641
Operating lease liability		$ 4,582		$ 4,582		5,804
Weighted average discount rate		10.00%		10.00%
Weighted average remaining operating lease term (in years)		3 years 9 months 18 days		3 years 9 months 18 days
Rent expense		$ 500	$ 500	$ 1,500	$ 1,500
Total minimum payments		55,141		55,141		56,716
Accounting Standards Update 2016-02
Guarantor Obligations
Operating lease right-of-use assets, net							$ 6,000
Operating lease liability							7,400
Contract with Customer, Liability							1,400
Cumulative Effect, Period of Adoption, Adjusted Balance | Accounting Standards Update 2016-02
Guarantor Obligations
Operating lease right-of-use assets, net							6,000
Operating lease liability							7,400
Contract with Customer, Liability							$ 1,400
Redwood City, CA
Guarantor Obligations
Operating lease term (in years)								3 years
Total minimum payments		$ 5,100		$ 5,100		$ 6,700
Line of Credit | Loan Facility
Guarantor Obligations
Interest only period	36 months					24 months