Commitments and Contingencies (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Contractual amount net of risk participations	$ 76,000	$ 83,000
Guarantee Obligations [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	9,046,307	8,845,199
Letters of Credit [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	156,187	150,948
Commitments to Fund Commercial Real Estate, Construction, and Land Development Loans [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,359,986	1,394,162
Unused Credit Card Lines [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,135,102	1,103,431
Commitments under Home Equity Lines of Credit [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,131,277	1,096,052
Commitments to Fund Commercial and Industrial Loans [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	4,960,671	4,792,834
Other Loan Commitments [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	$ 303,084	$ 307,772