Derivatives - Fair Values of Derivative Instruments on Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Assets	$ 20,390	$ 19,448
Derivatives not designated as hedging instruments, Fair Value, Gross Liability	21,219	20,455
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amounts	140,000	140,000
Derivatives not designated as hedging instruments, Fair Value, Gross Liability	126	298
Derivatives designated as hedging instruments [Member] | Interest rate swap [Member] | Cash Flow Hedges [Member]
Derivatives, Fair Value [Line Items]
Notional Amounts	140,000	140,000
Derivatives designated as hedging instruments [Member] | Other liabilities [Member] | Interest rate swap [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Liability	126	298
Derivatives not designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Amounts	791,871	720,868
Derivatives not designated as hedging instruments, Fair Value, Gross Assets	21,254	20,093
Derivatives not designated as hedging instruments, Fair Value, Gross Liability	21,949	20,802
Derivatives not designated as hedging instruments [Member] | Interest rate swap [Member]
Derivatives, Fair Value [Line Items]
Notional Amounts	593,703	547,477
Derivatives not designated as hedging instruments [Member] | Forward Commitments To Sell Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Notional Amounts	106,105	115,256
Derivatives not designated as hedging instruments [Member] | Interest Rate Lock Commitments On Residential Mortgage Loan [Member]
Derivatives, Fair Value [Line Items]
Notional Amounts	70,898	58,135
Derivatives not designated as hedging instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Notional Amounts	21,165
Derivatives not designated as hedging instruments [Member] | Other liabilities [Member] | Interest rate swap [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Liability	21,093	20,157
Derivatives not designated as hedging instruments [Member] | Other liabilities [Member] | Forward Commitments To Sell Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Liability	633	590
Derivatives not designated as hedging instruments [Member] | Other liabilities [Member] | Interest Rate Lock Commitments On Residential Mortgage Loan [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Liability	218	55
Derivatives not designated as hedging instruments [Member] | Other liabilities [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Liability	5
Derivatives not designated as hedging instruments [Member] | Other assets [Member] | Interest rate swap [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Assets	20,390	19,448
Derivatives not designated as hedging instruments [Member] | Other assets [Member] | Forward Commitments To Sell Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Assets	346	190
Derivatives not designated as hedging instruments [Member] | Other assets [Member] | Interest Rate Lock Commitments On Residential Mortgage Loan [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Assets	505	455
Derivatives not designated as hedging instruments [Member] | Other assets [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments, Fair Value, Gross Assets	$ 13