Loans and Allowance for Loan Losses - Summary of Activity in the Loan Balances and the Allowance for Loan Losses by Segment (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	$ 17,063	$ 16,136	$ 18,792
Losses charged off	(7,578)	(10,109)	(13,625)
Recoveries	910	683	744
Provision charged to expense	7,242	10,353	10,225
Balance, end of period	17,637	17,063	16,136
Ending allowance balance attributable to loans:
Individually evaluated for impairment	1,673	3,932	7,117
Collectively evaluated for impairment	15,964	13,131	9,019
Total ending allowance balance	17,637	17,063	16,136
Loans:
Individually evaluated for impairment	26,167	33,592	44,668
Collectively evaluated for impairment	856,381	809,496	767,911
Total ending loans balance	882,548	843,088	812,579
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	10,714	11,127	14,390
Losses charged off	(3,199)	(5,195)	(8,508)
Recoveries	388	280	87
Provision charged to expense	3,483	4,502	5,158
Balance, end of period	11,386	10,714	11,127
Ending allowance balance attributable to loans:
Individually evaluated for impairment	1,449	3,747	6,865
Collectively evaluated for impairment	9,937	6,967	4,262
Total ending allowance balance	11,386	10,714	11,127
Loans:
Individually evaluated for impairment	23,321	31,746	38,853
Collectively evaluated for impairment	390,684	350,106	336,950
Total ending loans balance	414,005	381,852	375,803
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	1,409	1,317	862
Losses charged off	(213)	(262)	(1,507)
Recoveries	45	42	157
Provision charged to expense	(406)	312	1,805
Balance, end of period	835	1,409	1,317
Ending allowance balance attributable to loans:
Individually evaluated for impairment	209	148	206
Collectively evaluated for impairment	626	1,261	1,111
Total ending allowance balance	835	1,409	1,317
Loans:
Individually evaluated for impairment	597	705	1,333
Collectively evaluated for impairment	68,108	75,865	64,329
Total ending loans balance	68,705	76,570	65,662
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	1,331	805	528
Losses charged off	(1,430)	(1,664)	(1,491)
Recoveries	96	22	30
Provision charged to expense	1,562	2,168	1,738
Balance, end of period	1,559	1,331	805
Ending allowance balance attributable to loans:
Individually evaluated for impairment	15	37	46
Collectively evaluated for impairment	1,544	1,294	759
Total ending allowance balance	1,559	1,331	805
Loans:
Individually evaluated for impairment	1,790	1,141	4,482
Collectively evaluated for impairment	63,193	63,383	70,203
Total ending loans balance	64,983	64,524	74,685
Home Equity Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	2,289	1,512	1,591
Losses charged off	(1,372)	(1,895)	(1,091)
Recoveries	35	62	39
Provision charged to expense	1,405	2,610	973
Balance, end of period	2,357	2,289	1,512
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	2,357	2,289	1,512
Total ending allowance balance	2,357	2,289	1,512
Loans:
Individually evaluated for impairment	398	0	0
Collectively evaluated for impairment	122,432	126,958	132,536
Total ending loans balance	122,830	126,958	132,536
Indirect
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	891	904	799
Losses charged off	(963)	(695)	(455)
Recoveries	288	209	293
Provision charged to expense	1,014	473	267
Balance, end of period	1,230	891	904
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	1,230	891	904
Total ending allowance balance	1,230	891	904
Loans:
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	199,924	180,089	150,031
Total ending loans balance	199,924	180,089	150,031
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	429	471	622
Losses charged off	(401)	(398)	(573)
Recoveries	58	68	138
Provision charged to expense	184	288	284
Balance, end of period	270	429	471
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	270	429	471
Total ending allowance balance	270	429	471
Loans:
Individually evaluated for impairment	61	0	0
Collectively evaluated for impairment	12,040	13,095	13,862
Total ending loans balance	$ 12,101	$ 13,095	$ 13,862