Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Carrying (Reported) Amount
Assets:
Cash and due from banks	$ 57,027	$ 73,312
Interest-bearing time deposits	35,324	52,851
Investment securities available for sale	551,619	518,491
Investment securities held to maturity	377,097	427,909
Mortgage loans held for sale	27,711	17,864
Loans	2,766,831	2,642,517
Federal Reserve Bank and Federal Home Loan Bank stock	32,824	31,270
Interest rate swap asset	6,618	5,665
Interest receivable	17,519	17,723
Liabilities:
Deposits	3,194,751	3,134,655
Borrowings:
Federal funds purchased	57,024
Securities sold under repurchase agreements	153,454	156,305
Federal Home Loan Bank advances	145,467	138,095
Subordinated debentures, revolving credit lines and term loans	112,169	194,974
Interest rate swap liability	10,406	7,797
Interest payable	1,591	2,925
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and due from banks	57,027	73,312
Interest-bearing time deposits	35,324	52,851
Liabilities:
Deposits	2,292,977	2,195,679
Significant Other Observable Inputs (Level 2)
Assets:
Investment securities available for sale	533,194	497,653
Investment securities held to maturity	385,155	428,737
Mortgage loans held for sale	27,711	17,864
Federal Reserve Bank and Federal Home Loan Bank stock	32,824	31,270
Interest rate swap asset	6,618
Interest receivable	17,519	17,723
Liabilities:
Deposits	902,678	944,078
Borrowings:
Federal funds purchased	57,024
Securities sold under repurchase agreements	154,017	157,342
Federal Home Loan Bank advances	148,985	141,693
Subordinated debentures, revolving credit lines and term loans	67,837	142,632
Interest rate swap liability	10,405
Interest payable	1,591	2,925
Significant Unobservable Inputs (Level 3)
Assets:
Investment securities available for sale	18,425	20,838
Investment securities held to maturity	11,062	13,732
Loans	2,793,212	2,658,227
Interest rate swap asset		5,665
Borrowings:
Interest rate swap liability		$ 7,797

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