Fair Value Measurements - Assets and Liabilities Held and their Related Classifications Under the Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets
Cash and cash equivalents	$ 24,141	$ 33,671
Total assets	24,141	33,671
Temporary Equity
Redeemable noncontrolling interests	12,500	12,500
Total temporary equity	12,500	12,500
(Level 1)
Assets
Cash and cash equivalents	24,141	33,671
Total assets	24,141	33,671
Temporary Equity
Redeemable noncontrolling interests	0	0
Total temporary equity	0	0
(Level 2)
Assets
Cash and cash equivalents	0	0
Total assets	0	0
Temporary Equity
Redeemable noncontrolling interests	0	0
Total temporary equity	0	0
(Level 3)
Assets
Cash and cash equivalents	0	0
Total assets	0	0
Temporary Equity
Redeemable noncontrolling interests	12,500	12,500
Total temporary equity	$ 12,500	$ 12,500