Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commercial | Real estate
Financing Receivable, Impaired [Line Items]
Recorded Balance	$ 5,549	$ 6,966
Unpaid Principal Balance	7,301	7,764
Specific Allowance	100	209
Average Investment in Impaired Loans	5,595	5,307	9,221
Interest Income Recognized	260	211	466
Commercial | Construction and development
Financing Receivable, Impaired [Line Items]
Recorded Balance	8,271	12,943
Unpaid Principal Balance	12,235	19,082
Specific Allowance	959	1,437
Average Investment in Impaired Loans	10,114	13,226	6,628
Interest Income Recognized	108	581	253
Commercial | Other
Financing Receivable, Impaired [Line Items]
Recorded Balance	1,884	5,500
Unpaid Principal Balance	1,884	5,691
Specific Allowance	257	543
Average Investment in Impaired Loans	3,749	1,726	388
Interest Income Recognized	147	271	12
Residential Mortgage
Financing Receivable, Impaired [Line Items]
Recorded Balance	3,417	5,915
Unpaid Principal Balance	4,356	7,407
Specific Allowance	57	36
Average Investment in Impaired Loans	4,409	5,599	4,708
Interest Income Recognized	58	178	183
Loans without a specific valuation allowance | Commercial | Real estate
Financing Receivable, Impaired [Line Items]
Recorded Balance	5,341	4,883
Unpaid Principal Balance	6,354	5,275
Average Investment in Impaired Loans	5,384	4,221	3,826
Interest Income Recognized	248	137	137
Loans without a specific valuation allowance | Commercial | Construction and development
Financing Receivable, Impaired [Line Items]
Recorded Balance	3,632	5,872
Unpaid Principal Balance	7,078	11,801
Average Investment in Impaired Loans	4,884	9,451	2,390
Interest Income Recognized	30	348	27
Loans without a specific valuation allowance | Commercial | Other
Financing Receivable, Impaired [Line Items]
Recorded Balance	972	4,030
Unpaid Principal Balance	972	4,167
Average Investment in Impaired Loans	2,828	1,480	388
Interest Income Recognized	117	211	12
Loans without a specific valuation allowance | Residential Mortgage
Financing Receivable, Impaired [Line Items]
Recorded Balance	2,583	5,378
Unpaid Principal Balance	3,522	6,870
Average Investment in Impaired Loans	3,755	5,532	4,580
Interest Income Recognized	58	142	183
Loans with a specific valuation allowance | Commercial | Real estate
Financing Receivable, Impaired [Line Items]
Recorded Balance	208	2,083
Unpaid Principal Balance	947	2,489
Specific Allowance	100	209
Average Investment in Impaired Loans	211	1,086	5,395
Interest Income Recognized	12	74	329
Loans with a specific valuation allowance | Commercial | Construction and development
Financing Receivable, Impaired [Line Items]
Recorded Balance	4,639	7,071
Unpaid Principal Balance	5,157	7,281
Specific Allowance	959	1,437
Average Investment in Impaired Loans	5,230	3,775	4,238
Interest Income Recognized	78	233	226
Loans with a specific valuation allowance | Commercial | Other
Financing Receivable, Impaired [Line Items]
Recorded Balance	912	1,470
Unpaid Principal Balance	912	1,524
Specific Allowance	257	543
Average Investment in Impaired Loans	921	246
Interest Income Recognized	30	60
Loans with a specific valuation allowance | Residential Mortgage
Financing Receivable, Impaired [Line Items]
Recorded Balance	834	537
Unpaid Principal Balance	834	537
Specific Allowance	57	36
Average Investment in Impaired Loans	654	67	128
Interest Income Recognized		$ 36