Fair Values Of Assets And Liabilities (Narrative) (Detail) - USD ($)		3 Months Ended	9 Months Ended
		Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		$ 2,214,281,000	$ 2,214,281,000	$ 1,792,078,000	$ 1,782,648,000
Mortgage loans held-for-sale, at fair value		347,005,000	347,005,000	351,290,000	363,303,000
Impaired loans—collateral based	[1]	$ 113,027,000	113,027,000	127,412,000	129,537,000
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount for Lack of Marketability		10.00%
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		$ 2,214,281,000	2,214,281,000	1,792,078,000	1,782,648,000
Mortgage servicing rights		7,875,000	7,875,000	8,435,000	8,137,000
Remaining contractual principal balance outstanding, mortgage loans held-for-sale		328,100,000	328,100,000	327,100,000	340,000,000
Mortgage loans held-for-sale, at fair value		347,005,000	347,005,000	351,290,000	363,303,000
Impaired loans—collateral based		73,800,000	73,800,000
Portion at Other than Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans—collateral based		39,200,000	39,200,000
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		297,342,000	297,342,000	238,529,000	187,103,000
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		54,004,000	54,004,000	51,139,000	52,155,000
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights		7,875,000	7,875,000	8,435,000	8,137,000
Mortgage loans held-for-sale, at fair value		347,005,000	347,005,000	351,290,000	363,303,000
Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		297,342,000	297,342,000	238,529,000	187,103,000
Fair Value, Measurements, Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		54,004,000	54,004,000	51,139,000	52,155,000
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans—collateral based		73,819,000	73,819,000
Other real estate owned	[2]	80,524,000	80,524,000
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights		7,875,000	7,875,000	8,435,000	8,137,000
Mortgage loans held-for-sale, at fair value		$ 0	0	0	0
Level 3 | Fair Value, Measurements, Recurring | Minimum | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate		9.00%
Fair Value Inputs, Prepayment Rate		9.00%
Level 3 | Fair Value, Measurements, Recurring | Maximum | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate		13.00%
Fair Value Inputs, Prepayment Rate		29.00%
Level 3 | Fair Value, Measurements, Recurring | Weighted Average | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate		9.15%
Fair Value Inputs, Prepayment Rate		12.93%
Level 3 | Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		$ 68,401,000	68,401,000	58,953,000	50,237,000
Level 3 | Fair Value, Measurements, Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value		$ 24,516,000	$ 24,516,000	23,711,000	23,961,000
Level 3 | Fair Value, Measurements, Recurring | Equity securities | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate		2.01%
Level 3 | Fair Value, Measurements, Recurring | Equity securities | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate		2.43%	2.43%
Level 3 | Fair Value, Measurements, Recurring | Equity securities | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate			2.22%
Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans—collateral based		$ 73,819,000	$ 73,819,000
Other real estate owned		$ 80,524,000	80,524,000
Level 3 | Fair Value, Measurements, Nonrecurring | Minimum | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount for Lack of Marketability		10.00%
Level 3 | Fair Value, Measurements, Nonrecurring | Maximum | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount for Lack of Marketability		10.00%
Non-performing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held-for-sale, at fair value		$ 0	$ 0	$ 0	$ 0

[1] Impaired loans are considered by the Company to be non-accrual loans, TDRs or loans with principal and/or interest at risk, even if the loan is current with all payments of principal and interest.

[2] Fair value losses recognized, net on other real estate owned include valuation adjustments and charge-offs during the respective period.