Commitments and Contingencies - Commitments and Letters of Credit (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Other Commitments [Line Items]
Commitments and letters of credit	$ 2,052,211	$ 1,990,845
Commitments to extend credit
Other Commitments [Line Items]
Commitments and letters of credit	1,967,190	1,910,805
Standby letters of credit
Other Commitments [Line Items]
Commitments and letters of credit	$ 85,021	$ 80,040