Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Carrying (Reported) Amount
Assets:
Cash and due from banks	$ 68,493	$ 73,312
Interest-bearing time deposits	41,760	52,851
Investment securities available for sale	547,551	518,491
Investment securities held to maturity	396,770	427,909
Mortgage loans held for sale	15,278	17,864
Loans	2,727,491	2,642,517
Federal Reserve Bank and Federal Home Loan Bank stock	33,033	31,270
Interest rate swap asset	5,795	5,665
Interest receivable	16,506	17,723
Liabilities:
Deposits	3,288,898	3,134,655
Borrowings:
Federal funds purchased	652
Securities sold under repurchase agreements	160,127	156,305
Federal Home Loan Bank advances	96,847	138,095
Subordinated debentures, revolving credit lines and term loans	115,951	194,974
Interest rate swap liability	9,136	7,797
Interest payable	2,168	2,925
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and due from banks	68,493	73,312
Interest-bearing time deposits	41,760	52,851
Liabilities:
Deposits	2,343,492	2,195,679
Significant Other Observable Inputs (Level 2)
Assets:
Investment securities available for sale	527,811	497,653
Investment securities held to maturity	400,173	428,737
Mortgage loans held for sale	15,278	17,864
Federal Reserve Bank and Federal Home Loan Bank stock	33,033	31,270
Interest rate swap asset	5,795
Interest receivable	16,506	17,723
Liabilities:
Deposits	946,039	944,078
Borrowings:
Federal funds purchased	652
Securities sold under repurchase agreements	160,728	157,342
Federal Home Loan Bank advances	100,031	141,693
Subordinated debentures, revolving credit lines and term loans	68,852	142,632
Interest rate swap liability	9,136
Interest payable	2,168	2,925
Significant Unobservable Inputs (Level 3)
Assets:
Investment securities available for sale	19,740	20,838
Investment securities held to maturity	13,074	13,732
Loans	2,756,565	2,658,227
Interest rate swap asset		5,665
Borrowings:
Interest rate swap liability		$ 7,797

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