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	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	$ 17,300	$ 17,351	$ 17,063	$ 16,136
Losses charged off	(1,681)	(1,751)	(5,378)	(6,362)
Recoveries	93	145	460	526
Provision charged to expense	1,875	2,100	5,442	7,545
Balance, end of period	17,587	17,845	17,587	17,845
Ending allowance balance attributable to loans:
Individually evaluated for impairment	2,596	6,070	2,596	6,070
Collectively evaluated for impairment	14,991	11,775	14,991	11,775
Total ending allowance balance	17,587	17,845	17,587	17,845
Loans:
Individually evaluated for impairment	26,829	38,246	26,829	38,246
Collectively evaluated for impairment	858,886	792,066	858,886	792,066
Total ending loans balance	885,715	830,312	885,715	830,312	843,088
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	11,396	11,681	10,714	11,127
Losses charged off	(738)	(577)	(2,057)	(2,669)
Recoveries	9	34	39	249
Provision charged to expense	1,093	648	3,064	3,079
Balance, end of period	11,760	11,786	11,760	11,786
Ending allowance balance attributable to loans:
Individually evaluated for impairment	2,525	5,602	2,525	5,602
Collectively evaluated for impairment	9,235	6,184	9,235	6,184
Total ending allowance balance	11,760	11,786	11,760	11,786
Loans:
Individually evaluated for impairment	25,310	35,349	25,310	35,349
Collectively evaluated for impairment	386,614	351,542	386,614	351,542
Total ending loans balance	411,924	386,891	411,924	386,891	381,852
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	840	1,182	1,409	1,317
Losses charged off	(48)	(13)	(213)	(236)
Recoveries	4	2	24	38
Provision charged to expense	(42)	(46)	(466)	6
Balance, end of period	754	1,125	754	1,125
Ending allowance balance attributable to loans:
Individually evaluated for impairment	69	166	69	166
Collectively evaluated for impairment	685	959	685	959
Total ending allowance balance	754	1,125	754	1,125
Loans:
Individually evaluated for impairment	340	771	340	771
Collectively evaluated for impairment	71,582	71,908	71,582	71,908
Total ending loans balance	71,922	72,679	71,922	72,679	76,570
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	1,716	1,249	1,331	805
Losses charged off	(292)	(443)	(1,267)	(1,746)
Recoveries	3	9	86	49
Provision charged to expense	274	435	1,551	2,142
Balance, end of period	1,701	1,250	1,701	1,250
Ending allowance balance attributable to loans:
Individually evaluated for impairment	2	302	2	302
Collectively evaluated for impairment	1,699	948	1,699	948
Total ending allowance balance	1,701	1,250	1,701	1,250
Loans:
Individually evaluated for impairment	1,179	2,126	1,179	2,126
Collectively evaluated for impairment	67,370	66,711	67,370	66,711
Total ending loans balance	68,549	68,837	68,549	68,837	64,524
Home Equity Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	2,146	1,891	2,289	1,512
Losses charged off	(296)	(548)	(851)	(957)
Recoveries	16	42	31	15
Provision charged to expense	264	929	661	1,744
Balance, end of period	2,130	2,314	2,130	2,314
Ending allowance balance attributable to loans:
Collectively evaluated for impairment	2,130	2,314	2,130	2,314
Total ending allowance balance	2,130	2,314	2,130	2,314
Loans:
Collectively evaluated for impairment	125,108	130,143	125,108	130,143
Total ending loans balance	125,108	130,143	125,108	130,143	126,958
Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	985	921	891	904
Losses charged off	(161)	(117)	(738)	(264)
Recoveries	54	44	244	77
Provision charged to expense	134	103	615	234
Balance, end of period	1,012	951	1,012	951
Ending allowance balance attributable to loans:
Collectively evaluated for impairment	1,012	951	1,012	951
Total ending allowance balance	1,012	951	1,012	951
Loans:
Collectively evaluated for impairment	195,358	158,885	195,358	158,885
Total ending loans balance	195,358	158,885	195,358	158,885	180,089
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	217	427	429	471
Losses charged off	(146)	(53)	(252)	(490)
Recoveries	7	14	36	98
Provision charged to expense	152	31	17	340
Balance, end of period	230	419	230	419
Ending allowance balance attributable to loans:
Collectively evaluated for impairment	230	419	230	419
Total ending allowance balance	230	419	230	419
Loans:
Collectively evaluated for impairment	12,854	12,877	12,854	12,877
Total ending loans balance	$ 12,854	$ 12,877	$ 12,854	$ 12,877	$ 13,095