Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Carrying (Reported) Amount
Assets:
Cash and due from banks	$ 51,592	$ 101,460
Interest-bearing time deposits	60,407	38,443
Investment securities available for sale	532,867	513,343
Investment securities held to maturity	336,696	361,020
Mortgage loans held for sale	26,555	22,300
Loans	2,811,005	2,832,843
Federal Reserve Bank and Federal Home Loan Bank stock	32,777	32,785
Interest rate swap asset	5,388	6,300
Interest receivable	15,346	16,367
Liabilities:
Deposits	3,310,808	3,346,383
Borrowings:
Federal funds purchased		18,862
Securities sold under repurchase agreements	161,813	141,828
Federal Home Loan Bank advances	93,169	94,238
Subordinated debentures, revolving credit lines and term loans	111,778	112,161
Interest rate swap liability	8,307	9,766
Interest payable	1,348	1,841
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and due from banks	51,592	101,460
Interest-bearing time deposits	60,407	38,443
Liabilities:
Deposits	2,481,769	2,478,706
Significant Other Observable Inputs (Level 2)
Assets:
Investment securities available for sale	515,189	495,015
Investment securities held to maturity	344,948	366,590
Mortgage loans held for sale	26,555	22,300
Federal Reserve Bank and Federal Home Loan Bank stock	32,777	32,785
Interest rate swap asset	5,388	6,300
Interest receivable	15,346	16,367
Liabilities:
Deposits	825,841	865,793
Borrowings:
Federal funds purchased		18,862
Securities sold under repurchase agreements	162,234	142,318
Federal Home Loan Bank advances	96,211	97,357
Subordinated debentures, revolving credit lines and term loans	62,596	62,133
Interest rate swap liability	8,307	9,766
Interest payable	1,348	1,841
Significant Unobservable Inputs (Level 3)
Assets:
Investment securities available for sale	17,678	18,328
Investment securities held to maturity	6,491	11,584
Loans	$ 2,824,164	$ 2,852,614

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