Summary of Significant Accounting Policies - Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Subsidiary, Sale of Stock [Line Items]
Total cash and cash equivalents	$ 320,484	$ 100,130	$ 113,347
Convertible preferred stock warrant liability	0	177
Fair Value, Measurements, Recurring
Subsidiary, Sale of Stock [Line Items]
Cash	179,797	1,502
Cash equivalents	140,687	98,628
Total cash and cash equivalents	320,484	100,130
Convertible preferred stock warrant liability	0	177
Loan facility derivative liability	1,610	1,782
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Subsidiary, Sale of Stock [Line Items]
Cash	179,797	1,502
Cash equivalents	140,687	98,628
Total cash and cash equivalents	320,484	100,130
Convertible preferred stock warrant liability	0	0
Loan facility derivative liability	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Subsidiary, Sale of Stock [Line Items]
Cash	0	0
Cash equivalents	0	0
Total cash and cash equivalents	0	0
Convertible preferred stock warrant liability	0	0
Loan facility derivative liability	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Subsidiary, Sale of Stock [Line Items]
Cash	0	0
Cash equivalents	0	0
Total cash and cash equivalents	0	0
Convertible preferred stock warrant liability	0	177
Loan facility derivative liability	$ 1,610	$ 1,782