Impaired Loans and Valuation Allowance for Loan Losses - Company's Average Recorded Investments in Impaired Loans and Related Interest Income (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, Total	$ 70,867	$ 99,678
Interest Income Recognized, Total	910	2,400
Construction and Land Development [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Average Recorded Investment	2,382	1,495
With No Related Allowance, Interest Income Recognized	79	1
With Related Allowance, Average Recorded Investment	1,410	3,637
With Related Allowance, Interest Income Recognized	30	98
Average Recorded Investment, Total	3,792	5,132
Interest Income Recognized, Total	109	99
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Average Recorded Investment	8,288	11,831
With No Related Allowance, Interest Income Recognized	14	326
With Related Allowance, Average Recorded Investment	20,144	42,769
With Related Allowance, Interest Income Recognized	319	1,204
Average Recorded Investment, Total	28,432	54,600
Interest Income Recognized, Total	333	1,530
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Average Recorded Investment	14,816	11,608
With No Related Allowance, Interest Income Recognized	40	129
With Related Allowance, Average Recorded Investment	23,105	27,223
With Related Allowance, Interest Income Recognized	406	617
Average Recorded Investment, Total	37,921	38,831
Interest Income Recognized, Total	446	746
Commercial and Financial [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Average Recorded Investment	3	9
With No Related Allowance, Interest Income Recognized	1	0
With Related Allowance, Average Recorded Investment	0	38
With Related Allowance, Interest Income Recognized	0	8
Average Recorded Investment, Total	3	47
Interest Income Recognized, Total	1	8
Consumer [Member]
Financing Receivable, Impaired [Line Items]
With No Related Allowance, Average Recorded Investment	140	463
With No Related Allowance, Interest Income Recognized	3	0
With Related Allowance, Average Recorded Investment	579	605
With Related Allowance, Interest Income Recognized	18	17
Average Recorded Investment, Total	719	1,068
Interest Income Recognized, Total	$ 21	$ 17