Impaired Loans and Valuation Allowance for Loan Losses - Activity in Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance, Beginning Balance	$ 20,078	$ 24,635	$ 22,104	$ 25,565
Provision for Loan Losses	1,180	900	2,698	9,660
Charge-Offs	(1,235)	(3,027)	(5,749)	(13,406)
Recoveries	393	611	1,363	1,300
Net Charge-Offs	(842)	(2,416)	(4,386)	(12,106)
Allowance, Ending Balance	20,416	23,119	20,416	23,119
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance, Beginning Balance	877	1,355	1,134	1,883
Provision for Loan Losses	(46)	(194)	121	(329)
Charge-Offs	(25)	(92)	(582)	(571)
Recoveries	41	210	174	296
Net Charge-Offs	16	118	(408)	(275)
Allowance, Ending Balance	847	1,279	847	1,279
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance, Beginning Balance	6,725	11,977	8,849	11,477
Provision for Loan Losses	377	225	(1)	6,285
Charge-Offs	(500)	(1,906)	(2,546)	(7,637)
Recoveries	239	117	539	288
Net Charge-Offs	(261)	(1,789)	(2,007)	(7,349)
Allowance, Ending Balance	6,841	10,413	6,841	10,413
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance, Beginning Balance	11,153	10,312	11,090	10,966
Provision for Loan Losses	750	950	2,388	3,856
Charge-Offs	(677)	(995)	(2,449)	(4,819)
Recoveries	83	234	330	498
Net Charge-Offs	(594)	(761)	(2,119)	(4,321)
Allowance, Ending Balance	11,309	10,501	11,309	10,501
Commercial and Financial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance, Beginning Balance	563	329	468	402
Provision for Loan Losses	72	(34)	(51)	116
Charge-Offs	0	0	(60)	(291)
Recoveries	24	40	302	108
Net Charge-Offs	24	40	242	(183)
Allowance, Ending Balance	659	335	659	335
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance, Beginning Balance	760	662	563	837
Provision for Loan Losses	27	(47)	291	(268)
Charge-Offs	(33)	(34)	(112)	(88)
Recoveries	6	10	18	110
Net Charge-Offs	(27)	(24)	(94)	22
Allowance, Ending Balance	$ 760	$ 591	$ 760	$ 591