Estimated Fair Value of Financial Instruments and Fair Value Measurement - Financial Assets and Liabilities are Classified (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets:
Investment securities, available for sale	$ 418,562	$ 393,710
Fair Value, Measurements, Recurring [Member]
Assets:
Investment securities, available for sale	418,562	393,710
Total Assets	418,923	393,905
Total Liabilities	361	195
Fair Value, Measurements, Recurring [Member] | Non-hedging [Member] | Interest Rate Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities	361	195
Assets:
Other Assets	361	195
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Investment securities, available for sale	7,107	5,503
Total Assets	7,107	5,503
Total Liabilities
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Non-hedging [Member] | Interest Rate Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities
Assets:
Other Assets
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investment securities, available for sale	411,455	388,207
Total Assets	411,816	388,402
Total Liabilities	361	195
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Non-hedging [Member] | Interest Rate Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities	361	195
Assets:
Other Assets	361	195
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Investment securities, available for sale
Total Assets
Total Liabilities
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Non-hedging [Member] | Interest Rate Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Liabilities
Assets:
Other Assets
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and U.S. Government Agencies [Member]
Assets:
Investment securities, available for sale	60,164	86,571
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and U.S. Government Agencies [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Investment securities, available for sale	4,366	3,493
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and U.S. Government Agencies [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investment securities, available for sale	55,798	83,078
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and U.S. Government Agencies [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Investment securities, available for sale
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed Securities, Residential [Member]
Assets:
Investment securities, available for sale	290,998	239,559
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed Securities, Residential [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Investment securities, available for sale
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed Securities, Residential [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investment securities, available for sale	290,998	239,559
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed Securities, Residential [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Investment securities, available for sale
Fair Value, Measurements, Recurring [Member] | Obligations of States and Political Subdivisions [Member]
Assets:
Investment securities, available for sale	37,691	38,620
Fair Value, Measurements, Recurring [Member] | Obligations of States and Political Subdivisions [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Investment securities, available for sale
Fair Value, Measurements, Recurring [Member] | Obligations of States and Political Subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investment securities, available for sale	37,691	38,620
Fair Value, Measurements, Recurring [Member] | Obligations of States and Political Subdivisions [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Investment securities, available for sale
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Assets:
Investment securities, available for sale	13,404	13,444
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Investment securities, available for sale
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investment securities, available for sale	13,404	13,444
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Investment securities, available for sale
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Assets:
Investment securities, available for sale	16,305	15,516
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Investment securities, available for sale	2,741	2,010
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investment securities, available for sale	13,564	13,506
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Investment securities, available for sale