Loans - Age Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Noncancelable Obligations Future Minimum Payments Due [Line Items]
30-59 Days Past Due	$ 3,749	$ 4,461
60-89 Days Past Due	726	3,868
Greater Than 90 Days	4,391	13,362
Total Past Due	8,866	21,691
Current	585,696	642,360
Total	594,562	664,051
Recorded Investment > 90 Days and Accruing	0	0
Commercial [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
30-59 Days Past Due	13	312
60-89 Days Past Due	0	59
Greater Than 90 Days	250	0
Total Past Due	263	371
Current	168,930	231,905
Total	169,193	232,276
Recorded Investment > 90 Days and Accruing	0	0
Commercial real estate: Construction [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
30-59 Days Past Due	0	0
60-89 Days Past Due	0	0
Greater Than 90 Days	0	0
Total Past Due	0	0
Current	15,625	16,863
Total	15,625	16,863
Recorded Investment > 90 Days and Accruing	0	0
Commercial real estate: Other [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
30-59 Days Past Due	1,102	1,265
60-89 Days Past Due	0	2,326
Greater Than 90 Days	0	8,343
Total Past Due	1,102	11,934
Current	287,529	274,469
Total	288,631	286,403
Recorded Investment > 90 Days and Accruing	0	0
Residential: 1-4 family [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
30-59 Days Past Due	2,382	2,758
60-89 Days Past Due	701	1,460
Greater Than 90 Days	4,141	5,019
Total Past Due	7,224	9,237
Current	65,880	69,320
Total	73,104	78,557
Recorded Investment > 90 Days and Accruing	0	0
Residential: Home equities [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
30-59 Days Past Due	249	126
60-89 Days Past Due	25	23
Greater Than 90 Days	0	0
Total Past Due	274	149
Current	43,715	45,032
Total	43,989	45,181
Recorded Investment > 90 Days and Accruing	0	0
Consumer [Member]
Noncancelable Obligations Future Minimum Payments Due [Line Items]
30-59 Days Past Due	3	0
60-89 Days Past Due	0	0
Greater Than 90 Days	0	0
Total Past Due	3	0
Current	4,017	4,771
Total	4,020	4,771
Recorded Investment > 90 Days and Accruing	$ 0	$ 0