Troubled Debts Restructured (Detail) (Troubled debts restructured, USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012 Investment	Sep. 30, 2011 Investment	Sep. 30, 2012 Investment	Sep. 30, 2011 Investment
Commercial | Real estate
Financing Receivable, Modifications [Line Items]
No. of Loans	1	1	4	1
Pre-Modification Outstanding Recorded Balance	$ 439	$ 113	$ 1,359	$ 113
Post-Modification Outstanding Recorded Balance	439	70	1,520	70
Commercial | Construction and Land Development
Financing Receivable, Modifications [Line Items]
No. of Loans	1		1	2
Pre-Modification Outstanding Recorded Balance	172		172	3,728
Post-Modification Outstanding Recorded Balance	172		172	3,728
Commercial | Other
Financing Receivable, Modifications [Line Items]
No. of Loans	2		5	1
Pre-Modification Outstanding Recorded Balance	46		262	103
Post-Modification Outstanding Recorded Balance	46		324	103
Residential Mortgage
Financing Receivable, Modifications [Line Items]
No. of Loans	10	6	28	22
Pre-Modification Outstanding Recorded Balance	719	463	2,455	2,529
Post-Modification Outstanding Recorded Balance	734	492	2,596	2,598
Consumer loans | Real estate
Financing Receivable, Modifications [Line Items]
No. of Loans	14	10	24	22
Pre-Modification Outstanding Recorded Balance	439	231	830	555
Post-Modification Outstanding Recorded Balance	438	231	830	551
Consumer loans | Other
Financing Receivable, Modifications [Line Items]
No. of Loans	2		4	1
Pre-Modification Outstanding Recorded Balance	36		53	14
Post-Modification Outstanding Recorded Balance	36		52	1
Consumer loans | Auto
Financing Receivable, Modifications [Line Items]
No. of Loans	2	1	3	1
Pre-Modification Outstanding Recorded Balance	9	10	16	10
Post-Modification Outstanding Recorded Balance	8	10	15	10
Consumer loans | Boat/RV
Financing Receivable, Modifications [Line Items]
No. of Loans	4	4	7	12
Pre-Modification Outstanding Recorded Balance	96	134	154	364
Post-Modification Outstanding Recorded Balance	$ 95	$ 133	$ 153	$ 357