Impaired Loans and Valuation Allowance for Loan Losses - Loan Portfolio and Related Allowance (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	$ 52,969	$ 82,901
Individually Evaluated for Impairment, Associated Allowance	5,446	7,269
Collectively Evaluated for Impairment, Carrying Value	1,251,238	1,143,180
Collectively Evaluated for Impairment, Associated Allowance	14,622	14,835
Carrying Value, Total	1,304,207	1,226,081
Associated Allowance, Total	20,068	22,104	25,565	37,744
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	3,681	4,025
Individually Evaluated for Impairment, Associated Allowance	149	230
Collectively Evaluated for Impairment, Carrying Value	63,769	56,711
Collectively Evaluated for Impairment, Associated Allowance	659	904
Carrying Value, Total	67,450	60,736
Associated Allowance, Total	808	1,134	1,883	7,214
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	12,418	38,487
Individually Evaluated for Impairment, Associated Allowance	638	2,264
Collectively Evaluated for Impairment, Carrying Value	507,964	448,341
Collectively Evaluated for Impairment, Associated Allowance	5,522	6,585
Carrying Value, Total	520,382	486,828
Associated Allowance, Total	6,160	8,849	11,477	18,563
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	35,731	39,719
Individually Evaluated for Impairment, Associated Allowance	4,528	4,700
Collectively Evaluated for Impairment, Carrying Value	557,015	529,612
Collectively Evaluated for Impairment, Associated Allowance	7,131	6,390
Carrying Value, Total	592,746	569,331
Associated Allowance, Total	11,659	11,090	10,966	10,102
Commercial and Financial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	166	0
Individually Evaluated for Impairment, Associated Allowance	13	0
Collectively Evaluated for Impairment, Carrying Value	78,470	61,903
Collectively Evaluated for Impairment, Associated Allowance	697	468
Carrying Value, Total	78,636	61,903
Associated Allowance, Total	710	468	402	480
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment, Carrying Value	973	670
Individually Evaluated for Impairment, Associated Allowance	118	75
Collectively Evaluated for Impairment, Carrying Value	44,020	46,613
Collectively Evaluated for Impairment, Associated Allowance	613	488
Carrying Value, Total	44,993	47,283
Associated Allowance, Total	$ 731	$ 563	$ 837	$ 1,385