Fair Value Disclosures (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 2,192,615,000		$ 2,375,224,000
Derivatives, Assets	22,339,000		24,316,000
Derivatives, Liabilities	35,668,000		50,247,000
Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	2,214,954,000		2,399,540,000
Total Liabilities	35,668,000		50,247,000
Designated As Hedging Instrument [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	725,000	[1]	1,419,000	[1]
Derivatives, Liabilities	17,506,000	[2]	31,662,000	[2]
Not Designated As Hedging Instruments [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	21,614,000	[1]	22,897,000	[1]
Derivatives, Liabilities	18,162,000	[2]	18,585,000	[2]
U.S. Government Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	93,716,000		110,148,000
U.S. Government Agencies [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	93,716,000		110,148,000
Obligations Of States And Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	396,343,000		398,510,000
Obligations Of States And Political Subdivisions [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	396,343,000		398,510,000
Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	1,635,299,000		1,778,192,000
Agency Residential Mortgage-Backed Securities [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	1,635,299,000		1,778,192,000
Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	304,000		565,000
Non-Agency Residential Mortgage-Backed Securities [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	304,000		565,000
Commercial Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	5,837,000		8,734,000
Commercial Mortgage Backed Securities [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	5,837,000		8,734,000
Other Structured Financial Products [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	11,761,000		11,297,000
Other Structured Financial Products [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	11,761,000		11,297,000
Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	24,921,000		44,086,000
Other Debt Securities [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	24,921,000		44,086,000
Other Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	24,434,000		23,692,000
Other Equity Securities [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	24,434,000		23,692,000
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	21,665,000		20,895,000
Derivatives, Assets	0		0
Derivatives, Liabilities	0		0
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	21,665,000		20,895,000
Total Liabilities	0		0
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Designated As Hedging Instrument [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	0	[1]	0	[1]
Derivatives, Liabilities	0	[2]	0	[2]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | Not Designated As Hedging Instruments [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	0	[1]	0	[1]
Derivatives, Liabilities	0	[2]	0	[2]
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member] | U.S. Government Agencies [Member] | Measured On Recurring Basis [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] | Measured On Recurring Basis [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] | Measured On Recurring Basis [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] | Measured On Recurring Basis [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] | Measured On Recurring Basis [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] | Measured On Recurring Basis [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] | Measured On Recurring Basis [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] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	21,665,000		20,895,000
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	2,156,420,000		2,340,235,000
Derivatives, Assets	22,339,000		24,316,000
Derivatives, Liabilities	35,668,000		50,247,000
Significant Other Observable Inputs (Level 2) [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	2,178,759,000		2,364,551,000
Total Liabilities	35,668,000		50,247,000
Significant Other Observable Inputs (Level 2) [Member] | Designated As Hedging Instrument [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	725,000	[1]	1,419,000	[1]
Derivatives, Liabilities	17,506,000	[2]	31,662,000	[2]
Significant Other Observable Inputs (Level 2) [Member] | Not Designated As Hedging Instruments [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	21,614,000	[1]	22,897,000	[1]
Derivatives, Liabilities	18,162,000	[2]	18,585,000	[2]
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Agencies [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	93,716,000		110,148,000
Significant Other Observable Inputs (Level 2) [Member] | Obligations Of States And Political Subdivisions [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	396,343,000		398,510,000
Significant Other Observable Inputs (Level 2) [Member] | Agency Residential Mortgage-Backed Securities [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	1,635,299,000		1,778,192,000
Significant Other Observable Inputs (Level 2) [Member] | Non-Agency Residential Mortgage-Backed Securities [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	304,000		565,000
Significant Other Observable Inputs (Level 2) [Member] | Commercial Mortgage Backed Securities [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	5,837,000		8,734,000
Significant Other Observable Inputs (Level 2) [Member] | Other Structured Financial Products [Member] | Measured On Recurring Basis [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] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	24,921,000		44,086,000
Significant Other Observable Inputs (Level 2) [Member] | Other Equity Securities [Member] | Measured On Recurring Basis [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]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	14,530,000		14,094,000
Derivatives, Assets	0		0
Derivatives, Liabilities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	14,530,000		14,094,000
Total Liabilities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Designated As Hedging Instrument [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	0	[1]	0	[1]
Derivatives, Liabilities	0	[2]	0	[2]
Significant Unobservable Inputs (Level 3) [Member] | Not Designated As Hedging Instruments [Member] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivatives, Assets	0	[1]	0	[1]
Derivatives, Liabilities	0	[2]	0	[2]
Significant Unobservable Inputs (Level 3) [Member] | U.S. Government Agencies [Member] | Measured On Recurring Basis [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] | Measured On Recurring Basis [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] | Measured On Recurring Basis [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] | Measured On Recurring Basis [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] | Commercial Mortgage Backed Securities [Member] | Measured On Recurring Basis [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] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	11,761,000		11,297,000
Significant Unobservable Inputs (Level 3) [Member] | Other Debt Securities [Member] | Measured On Recurring Basis [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] | Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 2,769,000		$ 2,797,000

[1] Included in Other assets

[2] Included in Other liabilities