Fair Value - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading securities	$ 3,331	$ 3,097	$ 2,918
Total investment securities - available-for-sale	2,659,084	2,500,784	2,208,262
U.S. Treasury [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	14,366	11,841
U.S. Government-Sponsored Entities and Agencies [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	374,956	517,325
Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	1,392,512	1,163,788
Mortgage-Backed Securities - Non-Agency [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	20,357	30,196
States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	643,887	577,324
Pooled Trust Preferred Securities Group 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	9,152	9,359
Other Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	203,854	190,951
Residential Loans Held for Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	13,572	12,591
Derivative Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative assets	26,722	36,512
Derivative Liability [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liabilities	21,217	30,010
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading securities	3,331	3,097
Fair Value, Inputs, Level 1 [Member] | U.S. Treasury [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	14,366	11,841
Fair Value, Inputs, Level 1 [Member] | Other Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	31,470	32,762
Fair Value, Inputs, Level 2 [Member] | U.S. Government-Sponsored Entities and Agencies [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	374,956	517,325
Fair Value, Inputs, Level 2 [Member] | Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	1,392,512	1,163,788
Fair Value, Inputs, Level 2 [Member] | Mortgage-Backed Securities - Non-Agency [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	20,357	30,196
Fair Value, Inputs, Level 2 [Member] | States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	643,211	576,340
Fair Value, Inputs, Level 2 [Member] | Other Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	172,384	158,189
Fair Value, Inputs, Level 2 [Member] | Residential Loans Held for Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	13,572	12,591
Fair Value, Inputs, Level 2 [Member] | Derivative Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative assets	26,722	36,512
Fair Value, Inputs, Level 2 [Member] | Derivative Liability [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liabilities	21,217	30,010
Fair Value, Inputs, Level 3 [Member] | States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	676	984
Fair Value, Inputs, Level 3 [Member] | Pooled Trust Preferred Securities Group 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	$ 9,152	$ 9,359