Commitments and Contingencies - Commitments and Letters of Credit (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Other Commitments [Line Items]
Commitments and letters of credit	$ 2,349,641	$ 2,274,847
Commitments to extend credit
Other Commitments [Line Items]
Commitments and letters of credit	2,261,223	2,185,752
Standby letters of credit
Other Commitments [Line Items]
Commitments and letters of credit	$ 88,418	$ 89,095