Fair Value Disclosures (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	$ 2,425,316		$ 2,603,816
Derivatives, Liabilities	67,111	[1]	72,126	[1]
Designated As Hedging Instrument [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	934	[2]	878	[2]
Derivatives, Liabilities	46,894	[1]	51,172	[1]
Not Designated As Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	23,756	[2]	25,037	[2]
Derivatives, Liabilities	20,217	[1]	20,954	[1]
U.S. Government Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	114,136		114,408
Obligations Of States And Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	426,444		435,777
Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	1,716,976		1,880,562
Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	26,238		27,450
Commercial Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	36,894		40,380
Other Structured Financial Products [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	9,977		9,550
Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	45,500		45,255
Other Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	24,461		24,519
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	1,418		21,266
Derivatives, Liabilities	0	[1]	0	[1]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Designated As Hedging Instrument [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	0	[2]	0	[2]
Derivatives, Liabilities	0	[1]	0	[1]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Not Designated As Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	0	[2]	0	[2]
Derivatives, Liabilities	0	[1]	0	[1]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | U.S. Government Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Obligations Of States And Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Other Structured Financial Products [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Other Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	1,418		21,266
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	2,385,172		2,543,044
Derivatives, Liabilities	67,111	[1]	72,126	[1]
Significant Other Observable Inputs (Level 2) [Member] | Designated As Hedging Instrument [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	934	[2]	878	[2]
Derivatives, Liabilities	46,894	[1]	51,172	[1]
Significant Other Observable Inputs (Level 2) [Member] | Not Designated As Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	23,756	[2]	25,037	[2]
Derivatives, Liabilities	20,217	[1]	20,954	[1]
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	114,136		114,408
Significant Other Observable Inputs (Level 2) [Member] | Obligations Of States And Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	426,444		435,777
Significant Other Observable Inputs (Level 2) [Member] | Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	1,716,976		1,880,562
Significant Other Observable Inputs (Level 2) [Member] | Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	646		650
Significant Other Observable Inputs (Level 2) [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	36,894		40,380
Significant Other Observable Inputs (Level 2) [Member] | Other Structured Financial Products [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Significant Other Observable Inputs (Level 2) [Member] | Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	45,500		45,255
Significant Other Observable Inputs (Level 2) [Member] | Other Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	19,886		97
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	38,726		39,506
Derivatives, Liabilities	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Designated As Hedging Instrument [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	0	[2]	0	[2]
Derivatives, Liabilities	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Not Designated As Hedging Instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	0	[2]	0	[2]
Derivatives, Liabilities	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | U.S. Government Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Obligations Of States And Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	25,592		26,800
Significant Unobservable Inputs (Level 3) [Member] | Commercial Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Other Structured Financial Products [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	9,977		9,550
Significant Unobservable Inputs (Level 3) [Member] | Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Other Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 3,157		$ 3,156

[1] Included in Other liabilities

[2] Included in Other assets