Fair Value Disclosures (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Detail) (USD $)	Jun. 30, 2014		Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 2,183,093,000		$ 2,375,224,000
Derivatives, Assets	24,586,000		24,316,000
Derivatives, Liabilities	43,164,000		50,247,000
Measured On Recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	2,207,679,000		2,399,540,000
Total Liabilities	43,164,000		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	641,000	[1]	1,419,000	[1]
Derivatives, Liabilities	23,570,000	[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	23,945,000	[1]	22,897,000	[1]
Derivatives, Liabilities	19,594,000	[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	95,877,000		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	95,877,000		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	399,263,000		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	399,263,000		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	1,620,775,000		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	1,620,775,000		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	381,000		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	381,000		565,000
Commercial Mortgage Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	5,882,000		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	5,882,000		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	11,995,000		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	11,995,000		11,297,000
Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	24,638,000		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	24,638,000		44,086,000
Other Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities	24,282,000		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	24,282,000		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	21,479,000		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	21,479,000		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	21,479,000		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	2,146,816,000		2,340,235,000
Derivatives, Assets	24,586,000		24,316,000
Derivatives, Liabilities	43,164,000		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	2,171,402,000		2,364,551,000
Total Liabilities	43,164,000		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	641,000	[1]	1,419,000	[1]
Derivatives, Liabilities	23,570,000	[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	23,945,000	[1]	22,897,000	[1]
Derivatives, Liabilities	19,594,000	[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	95,877,000		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	399,263,000		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	1,620,775,000		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	381,000		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	5,882,000		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	24,638,000		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	14,798,000		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	14,798,000		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	11,995,000		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	$ 2,803,000		$ 2,797,000

[1] Included in Other assets

[2] Included in Other liabilities