Commitments and Contingencies (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Contractual amount net of risk participations	$ 63,000	$ 83,000
Guarantee obligations
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	9,256,449	8,845,199
Letters of credit
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	152,082	150,948
Commitments to fund commercial real estate, construction, and land development loans
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,309,144	1,394,162
Unused credit card lines
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,170,429	1,103,431
Commitments under home equity lines of credit
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,133,569	1,096,052
Commitments to fund commercial and industrial loans
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	5,164,553	4,792,834
Other loan commitments
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	$ 326,672	$ 307,772