Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets:
Securities	$ 612,396	$ 516,844
Loans Held-for-Sale	18,993	21,485
Derivatives	209
Financial Liabilities Derivatives	214
U.S. Treasury and Agency Securities [Member]
Assets:
Securities	3,625	6,422
Corporate Securities [Member]
Assets:
Securities	0	1,005
Obligations of State and Political Subdivisions [Member]
Assets:
Securities	74,853	64,799
Mortgage-backed Securities - Residential [Member]
Assets:
Securities	533,212	443,934
Equity Securities [Member]
Assets:
Securities	706	684
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Securities	353	331
Loans Held-for-Sale	0	0
Derivatives	0
Financial Liabilities Derivatives	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury and Agency Securities [Member]
Assets:
Securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Securities [Member]
Assets:
Securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Obligations of State and Political Subdivisions [Member]
Assets:
Securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage-backed Securities - Residential [Member]
Assets:
Securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Securities [Member]
Assets:
Securities	353	331
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Securities	599,890	510,383
Loans Held-for-Sale	18,993	21,485
Derivatives	209
Financial Liabilities Derivatives	214
Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury and Agency Securities [Member]
Assets:
Securities	3,625	6,422
Significant Other Observable Inputs (Level 2) [Member] | Corporate Securities [Member]
Assets:
Securities	0	0
Significant Other Observable Inputs (Level 2) [Member] | Obligations of State and Political Subdivisions [Member]
Assets:
Securities	63,053	60,027
Significant Other Observable Inputs (Level 2) [Member] | Mortgage-backed Securities - Residential [Member]
Assets:
Securities	533,212	443,934
Significant Other Observable Inputs (Level 2) [Member] | Equity Securities [Member]
Assets:
Securities	0	0
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Securities	12,153	6,130
Loans Held-for-Sale	0	0
Derivatives	0
Financial Liabilities Derivatives	0
Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury and Agency Securities [Member]
Assets:
Securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Securities [Member]
Assets:
Securities	0	1,005
Significant Unobservable Inputs (Level 3) [Member] | Obligations of State and Political Subdivisions [Member]
Assets:
Securities	11,800	4,772
Significant Unobservable Inputs (Level 3) [Member] | Mortgage-backed Securities - Residential [Member]
Assets:
Securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member]
Assets:
Securities	$ 353	$ 353