Commitments and Contingencies - Years In Which Commitments are Expected to be Paid (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Other Commitments [Line Items]
Commitments to contribute capital to small business investment companies and CRA-related loan pools	$ 78,551	$ 55,499
2020
Other Commitments [Line Items]
Commitments to contribute capital to small business investment companies and CRA-related loan pools	34,229
2021
Other Commitments [Line Items]
Commitments to contribute capital to small business investment companies and CRA-related loan pools	35,112
2023
Other Commitments [Line Items]
Commitments to contribute capital to small business investment companies and CRA-related loan pools	3,652
2024
Other Commitments [Line Items]
Commitments to contribute capital to small business investment companies and CRA-related loan pools	$ 5,558