Commitments and Contingencies - Commitments and letters of credit (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Supply Commitment [Line Items]
Commitments and letters of credit	$ 2,044,774	$ 1,894,124
Low Income Housing Tax Credit [Member]
Supply Commitment [Line Items]
Commitments and letters of credit	28,480	46,507
Commitments to extend credit
Supply Commitment [Line Items]
Commitments and letters of credit	1,864,947	1,712,032
Standby letters of credit
Supply Commitment [Line Items]
Commitments and letters of credit	113,720	69,763
Other letters of credit
Supply Commitment [Line Items]
Commitments and letters of credit	$ 37,627	$ 65,822