Commitments and Contingencies (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Contractual amount net of risk participations	$ 63,000	$ 66,000
Guarantee Obligations [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	8,638,140	8,535,148
Standby and Commercial Letters of Credit [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	191,766	166,936
Commitments to Fund Commercial Real Estate, Construction, and Land Development Loans [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,852,670	1,882,130
Unused Credit Card Lines [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,057,833	1,055,181
Commitments under Home Equity Lines of Credit [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	1,073,028	1,051,386
Commitments to Fund Commercial and Industrial Loans [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	4,168,486	4,094,809
Other Loan Commitments [Member]
Loss Contingencies [Line Items]
Total unfunded lending commitments and letters of credit	$ 294,357	$ 284,706