Commitments and Contingencies - Commitments and Letters of Credit (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Other Commitments [Line Items]
Commitments and letters of credit	$ 2,590,791	$ 2,274,847
Commitments to extend credit
Other Commitments [Line Items]
Commitments and letters of credit	2,500,541	2,185,752
Standby letters of credit
Other Commitments [Line Items]
Commitments and letters of credit	$ 90,250	$ 89,095