Fair Value Measurements - Schedule of fair value on recurring basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Warrant liabilities
Warrant liabilities, non-current	$ 4,149	$ 15,389
Recurring
Warrant liabilities
Total	4,150,000	15,389
Recurring | Level 2 | 5-Year Private Warrants
Warrant liabilities
Warrant liabilities, non-current	4,125,000	15,327
Recurring | Level 2 | Seller Warrants
Warrant liabilities
Warrant liabilities, non-current	$ 25,000	$ 62