Commitments and Contingencies (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Contractual amount net of risk participations	$ 60,000,000	$ 77,000,000
Minimum
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	0
Maximum
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	5,000,000
Guarantee obligations
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	9,166,920,000	9,080,108,000
Letters of credit
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	175,164,000	153,372,000
Commitments to fund commercial and industrial loans
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	5,143,323,000	5,090,827,000
Commitments to fund commercial real estate, construction, and land development loans
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,541,810,000	1,567,583,000
Commitments under home equity lines of credit
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,156,283,000	1,137,714,000
Unused credit card lines
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	780,704,000	779,254,000
Other loan commitments
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	$ 369,636,000	$ 351,358,000