Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 13,570	$ 17,126
60-89 Days Past Due	3,388	5,100
Greater Than 90 Days	15,997	18,079
Total Past Due	32,955	40,305
Current	942,602	950,264
Total loans	975,557	990,569
Total Loans > 90 Days and Accruing	813	273
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	287,383	288,848
Commercial | Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,969	1,097
60-89 Days Past Due		992
Greater Than 90 Days	2,686	2,350
Total Past Due	4,655	4,439
Current	197,391	199,174
Total loans	202,046	203,613
Commercial | Construction and development
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	520	192
Greater Than 90 Days	4,702	4,912
Total Past Due	5,222	5,104
Current	11,839	12,358
Total loans	17,061	17,462
Commercial | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,191	259
60-89 Days Past Due		223
Greater Than 90 Days	729	735
Total Past Due	1,920	1,217
Current	66,356	66,556
Total loans	68,276	67,773
Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	7,522	12,487
60-89 Days Past Due	2,226	2,732
Greater Than 90 Days	6,295	8,356
Total Past Due	16,043	23,575
Current	475,090	479,044
Total loans	491,133	502,619
Total Loans > 90 Days and Accruing	813	177
Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	197,041	199,102
Consumer loans | Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	875	1,302
60-89 Days Past Due	358	358
Greater Than 90 Days	1,183	1,119
Total Past Due	2,416	2,779
Current	98,045	97,737
Total loans	100,461	100,516
Consumer loans | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	153	234
60-89 Days Past Due	25	21
Greater Than 90 Days	49	95
Total Past Due	227	350
Current	6,066	6,248
Total loans	6,293	6,598
Total Loans > 90 Days and Accruing		96
Consumer loans | Auto
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	49	47
60-89 Days Past Due	28	18
Greater Than 90 Days	1	15
Total Past Due	78	80
Current	15,004	15,492
Total loans	15,082	15,572
Consumer loans | Boat/RV
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,291	1,508
60-89 Days Past Due	751	756
Greater Than 90 Days	352	497
Total Past Due	2,394	2,761
Current	72,811	73,655
Total loans	$ 75,205	$ 76,416