Carrying Amounts And Fair Values of Company's Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financial Assets
Investments held-to-maturity and other equity securities	$ 242,613	$ 249,450
Loans, net of allowance	2,523,823	2,488,171
Other assets	84,326	83,714
Financial Liabilities
Time Deposits	506,778	524,820
Securities sold under retail repurchase agreements and federal funds purchased	50,302	86,929
Advances from FHLB	405,000	405,058
Subordinated debentures	35,000	35,000
Financial Assets
Investments held-to-maturity and other equity securities	247,657	255,660
Loans, net of allowance	2,571,047	2,453,314
Other assets	84,326	83,714
Financial Liabilities
Time Deposits	509,570	528,074
Securities sold under retail repurchase agreements and federal funds purchased	50,302	86,929
Advances from FHLB	448,119	451,408
Subordinated debentures	9,791	9,919
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets
Investments held-to-maturity and other equity securities	0	0
Loans, net of allowance	0	0
Other assets	0	0
Financial Liabilities
Time Deposits	0	0
Securities sold under retail repurchase agreements and federal funds purchased	0	0
Advances from FHLB	0	0
Subordinated debentures	0	0
Significant Other Observable Inputs (Level 2)
Financial Assets
Investments held-to-maturity and other equity securities	247,657	255,660
Loans, net of allowance	0	0
Other assets	84,326	83,714
Financial Liabilities
Time Deposits	509,570	528,074
Securities sold under retail repurchase agreements and federal funds purchased	50,302	86,929
Advances from FHLB	448,119	451,408
Subordinated debentures	0	0
Significant Unobservable Inputs (Level 3)
Financial Assets
Investments held-to-maturity and other equity securities	0	0
Loans, net of allowance	2,571,047	2,453,314
Other assets	0	0
Financial Liabilities
Time Deposits	0	0
Securities sold under retail repurchase agreements and federal funds purchased	0	0
Advances from FHLB	0	0
Subordinated debentures	$ 9,791	$ 9,919