Impaired Loans and Valuation Allowance for Loan Losses - Company's Recorded Investments in Impaired Loans and the Related Valuation Allowances (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Recorded Investment, Total	$ 54,233	$ 82,901
Unpaid Principal Balance, Total	64,175	93,023
Related Valuation Allowance, Total	5,177	7,269
Construction and Land Development [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Recorded Investment	2,674	1,128
With No Related Allowance, Unpaid Principal Balance	3,301	1,608
With No Related Allowance, Related Valuation Allowance	0	0
With Related Allowance, Recorded Investment	1,181	2,897
With Related Allowance, Unpaid Principal Balance	1,261	2,941
With Related Allowance, Related Valuation Allowance	173	230
Recorded Investment, Total	3,855	4,025
Unpaid Principal Balance, Total	4,562	4,549
Related Valuation Allowance, Total	173	230
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Recorded Investment	4,755	12,357
With No Related Allowance, Unpaid Principal Balance	6,836	14,337
With No Related Allowance, Related Valuation Allowance	0	0
With Related Allowance, Recorded Investment	8,968	26,130
With Related Allowance, Unpaid Principal Balance	9,495	26,648
With Related Allowance, Related Valuation Allowance	684	2,264
Recorded Investment, Total	13,723	38,487
Unpaid Principal Balance, Total	16,331	40,985
Related Valuation Allowance, Total	684	2,264
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Recorded Investment	14,212	15,463
With No Related Allowance, Unpaid Principal Balance	20,224	22,022
With No Related Allowance, Related Valuation Allowance	0	0
With Related Allowance, Recorded Investment	21,741	24,256
With Related Allowance, Unpaid Principal Balance	22,295	24,752
With Related Allowance, Related Valuation Allowance	4,202	4,700
Recorded Investment, Total	35,953	39,719
Unpaid Principal Balance, Total	42,519	46,774
Related Valuation Allowance, Total	4,202	4,700
Commercial and Financial [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Recorded Investment	24	0
With No Related Allowance, Unpaid Principal Balance	24	0
With No Related Allowance, Related Valuation Allowance	0	0
With Related Allowance, Recorded Investment	0	0
With Related Allowance, Unpaid Principal Balance	0	0
With Related Allowance, Related Valuation Allowance	0	0
Recorded Investment, Total	24	0
Unpaid Principal Balance, Total	24	0
Related Valuation Allowance, Total	0	0
Consumer [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Recorded Investment	127	223
With No Related Allowance, Unpaid Principal Balance	166	255
With No Related Allowance, Related Valuation Allowance	0	0
With Related Allowance, Recorded Investment	551	447
With Related Allowance, Unpaid Principal Balance	573	460
With Related Allowance, Related Valuation Allowance	118	75
Recorded Investment, Total	678	670
Unpaid Principal Balance, Total	739	715
Related Valuation Allowance, Total	$ 118	$ 75