Fair Value Measurements - Balances of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	$ 1,271,927	$ 1,139,524
Assets measured at fair value, Available for sale equity securities	2,143	2,126
Assets measured at fair value, Available for sale securities	1,274,070	1,141,650
Derivative financial instruments	33,292	33,317
Assets measured at fair value, Total	1,307,362	1,174,967
Derivative financial instruments	40,165	43,369
Liabilities measured at fair value, Total	40,165	43,369
U.S. Government-Sponsored Entities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	264,681	330,985
States of the U.S. and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	14,505	17,002
Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	16,240	16,100
Agency Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	355,941	250,881
Agency Collateralized Mortgage Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	609,752	491,199
Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	1,679	1,762
Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	9,129
Financial Services Industry [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	2,078	2,061
Insurance Services Industry [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	65	65
Collateralized Debt Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities		31,595
Trading Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments	33,173	33,317
Not for Trading Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments	119
Trading Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments	33,105	33,236
Not for Trading Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments	7,060	10,133
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Assets measured at fair value, Available for sale equity securities	623	649
Assets measured at fair value, Available for sale securities	623	649
Derivative financial instruments
Assets measured at fair value, Total	623	649
Derivative financial instruments
Liabilities measured at fair value, Total
Level 1 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 1 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 1 [Member] | Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 1 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 1 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 1 [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 1 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 1 [Member] | Financial Services Industry [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	558	584
Level 1 [Member] | Insurance Services Industry [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	65	65
Level 1 [Member] | Collateralized Debt Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 1 [Member] | Trading Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments
Level 1 [Member] | Not for Trading Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments
Level 1 [Member] | Trading Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments
Level 1 [Member] | Not for Trading Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	1,270,264	1,106,185
Assets measured at fair value, Available for sale equity securities	1,106	1,067
Assets measured at fair value, Available for sale securities	1,271,370	1,107,252
Derivative financial instruments	33,292	33,317
Assets measured at fair value, Total	1,304,662	1,140,569
Derivative financial instruments	40,165	43,369
Liabilities measured at fair value, Total	40,165	43,369
Level 2 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	264,681	330,985
Level 2 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	14,505	17,002
Level 2 [Member] | Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	16,240	16,100
Level 2 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	355,941	250,881
Level 2 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	609,752	491,199
Level 2 [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	16	18
Level 2 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	9,129
Level 2 [Member] | Financial Services Industry [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	1,106	1,067
Level 2 [Member] | Insurance Services Industry [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities
Level 2 [Member] | Collateralized Debt Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 2 [Member] | Trading Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments	33,173	33,317
Level 2 [Member] | Not for Trading Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments	119
Level 2 [Member] | Trading Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments	33,105	33,236
Level 2 [Member] | Not for Trading Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments	7,060	10,133
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	1,663	33,339
Assets measured at fair value, Available for sale equity securities	414	410
Assets measured at fair value, Available for sale securities	2,077	33,749
Derivative financial instruments
Assets measured at fair value, Total	2,077	33,749
Derivative financial instruments
Liabilities measured at fair value, Total
Level 3 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 3 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 3 [Member] | Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 3 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 3 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 3 [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities	1,663	1,744
Level 3 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities
Level 3 [Member] | Financial Services Industry [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities	414	410
Level 3 [Member] | Insurance Services Industry [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale equity securities
Level 3 [Member] | Collateralized Debt Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Assets measured at fair value, Available for sale debt securities		31,595
Level 3 [Member] | Trading Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments
Level 3 [Member] | Not for Trading Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments
Level 3 [Member] | Trading Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments
Level 3 [Member] | Not for Trading Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative financial instruments