Fair Value Measurements - Financial Assets and Liabilities (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets:
Money market funds	$ 488,260	$ 0
Total assets	488,260	0
Liabilities:
Total liabilities	6,026	0
Contingent earn-out
Liabilities:
Contingent earn-out	6,026	0
Level 1
Assets:
Money market funds	488,260	328,195
Total assets	488,260	328,195
Liabilities:
Total liabilities	0	0
Level 1 | Contingent earn-out
Liabilities:
Contingent earn-out	0	0
Level 2
Assets:
Money market funds	0	0
Total assets	0	0
Liabilities:
Total liabilities	0	0
Level 2 | Contingent earn-out
Liabilities:
Contingent earn-out	0	0
Level 3
Assets:
Money market funds	0	0
Total assets	0	0
Liabilities:
Total liabilities	6,026	0
Level 3 | Contingent earn-out
Liabilities:
Contingent earn-out	$ 6,026	$ 0