Fair Value of Financial Instruments - Schedule of assets measured on a recurring basis at fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Cash equivalents
Total cash equivalents	$ 113,402	$ 6,771
Restricted cash equivalents
Total restricted cash equivalents	22,900	9,532
Marketable securities - restricted
Total marketable securities - restricted	62,625	24,651
Money market accounts
Cash equivalents
Total cash equivalents	113,402	6,771
Restricted cash equivalents
Total restricted cash equivalents	19,569	6,201
Certificates of deposits
Restricted cash equivalents
Total restricted cash equivalents	3,331	3,331
Corporate debt securities
Marketable securities - restricted
Total marketable securities - restricted	2,545	5,955
U.S. treasury and agency securities
Marketable securities - restricted
Total marketable securities - restricted	35,281	6,994
Commercial paper
Marketable securities - restricted
Total marketable securities - restricted	16,081	8,791
Asset backed securities
Marketable securities - restricted
Total marketable securities - restricted	8,718	2,911
Level 1
Cash equivalents
Total cash equivalents	113,402	6,771
Restricted cash equivalents
Total restricted cash equivalents	22,900	9,532
Marketable securities - restricted
Total marketable securities - restricted	33,295	6,994
Level 1 | Money market accounts
Cash equivalents
Total cash equivalents	113,402	6,771
Restricted cash equivalents
Total restricted cash equivalents	19,569	6,201
Level 1 | Certificates of deposits
Restricted cash equivalents
Total restricted cash equivalents	3,331	3,331
Level 1 | Corporate debt securities
Marketable securities - restricted
Total marketable securities - restricted	0	0
Level 1 | U.S. treasury and agency securities
Marketable securities - restricted
Total marketable securities - restricted	33,295	6,994
Level 1 | Commercial paper
Marketable securities - restricted
Total marketable securities - restricted	0	0
Level 1 | Asset backed securities
Marketable securities - restricted
Total marketable securities - restricted	0	0
Level 2
Cash equivalents
Total cash equivalents	0	0
Restricted cash equivalents
Total restricted cash equivalents	0	0
Marketable securities - restricted
Total marketable securities - restricted	29,330	17,657
Level 2 | Money market accounts
Cash equivalents
Total cash equivalents	0	0
Restricted cash equivalents
Total restricted cash equivalents	0	0
Level 2 | Certificates of deposits
Restricted cash equivalents
Total restricted cash equivalents	0	0
Level 2 | Corporate debt securities
Marketable securities - restricted
Total marketable securities - restricted	2,545	5,955
Level 2 | U.S. treasury and agency securities
Marketable securities - restricted
Total marketable securities - restricted	1,986	0
Level 2 | Commercial paper
Marketable securities - restricted
Total marketable securities - restricted	16,081	8,791
Level 2 | Asset backed securities
Marketable securities - restricted
Total marketable securities - restricted	8,718	2,911
Level 3
Cash equivalents
Total cash equivalents	0	0
Restricted cash equivalents
Total restricted cash equivalents	0	0
Marketable securities - restricted
Total marketable securities - restricted	0	0
Level 3 | Money market accounts
Cash equivalents
Total cash equivalents	0	0
Restricted cash equivalents
Total restricted cash equivalents	0	0
Level 3 | Certificates of deposits
Restricted cash equivalents
Total restricted cash equivalents	0	0
Level 3 | Corporate debt securities
Marketable securities - restricted
Total marketable securities - restricted	0	0
Level 3 | U.S. treasury and agency securities
Marketable securities - restricted
Total marketable securities - restricted	0	0
Level 3 | Commercial paper
Marketable securities - restricted
Total marketable securities - restricted	0	0
Level 3 | Asset backed securities
Marketable securities - restricted
Total marketable securities - restricted	$ 0	$ 0