Allowance for Loan Losses and Recorded Investment in Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Allowance for loan losses:
Beginning Balance	$ 2,697	$ 3,132	$ 2,400	$ 2,894
Provision charged to expense	126	225	387	657
Losses charged off	(123)	(360)	(216)	(634)
Recoveries	27	27	156	107
Ending Balance	2,727	3,024	2,727	3,024
Ending balance: individually evaluated for impairment	544	1,343	544	1,343	$ 714
Ending balance: collectively evaluated for impairment	2,183	1,681	2,183	1,681	1,686
Loans:
Ending balance: individually evaluated for impairment	1,816	5,878	1,816	5,878	1,868
Ending balance: collectively evaluated for impairment	324,509	306,866	324,509	306,866	313,886
Commercial
Allowance for loan losses:
Beginning Balance	234	472	254	412
Provision charged to expense	7	24	(39)	107
Losses charged off	0	0	0	(25)
Recoveries	0	1	26	3
Ending Balance	241	497	241	497
Ending balance: individually evaluated for impairment	84	354	84	354	92
Ending balance: collectively evaluated for impairment	157	143	157	143	162
Loans:
Ending balance: individually evaluated for impairment	96	437	96	437	112
Ending balance: collectively evaluated for impairment	61,625	46,494	61,625	46,494	52,174
Commercial Real Estate
Allowance for loan losses:
Beginning Balance	771	1,838	1,116	1,609
Provision charged to expense	(28)	(171)	(380)	45
Losses charged off	0	(205)	0	(205)
Recoveries	4	11	11	24
Ending Balance	747	1,473	747	1,473
Ending balance: individually evaluated for impairment	331	989	331	989	622
Ending balance: collectively evaluated for impairment	416	484	416	484	494
Loans:
Ending balance: individually evaluated for impairment	1,496	5,441	1,496	5,441	1,756
Ending balance: collectively evaluated for impairment	161,726	153,760	161,726	153,760	156,558
Residential
Allowance for loan losses:
Beginning Balance	172	91	92	90
Provision charged to expense	14	47	80	116
Losses charged off	(20)	(48)	(20)	(119)
Recoveries	7	1	21	4
Ending Balance	173	91	173	91
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	173	91	173	91	92
Loans:
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	83,200	83,761	83,200	83,761	83,870
Installment
Allowance for loan losses:
Beginning Balance	276	146	147	141
Provision charged to expense	46	93	186	214
Losses charged off	(103)	(107)	(196)	(285)
Recoveries	16	14	98	76
Ending Balance	235	146	235	146
Ending balance: individually evaluated for impairment	129	0	129	0	0
Ending balance: collectively evaluated for impairment	106	146	106	146	147
Loans:
Ending balance: individually evaluated for impairment	224	0	224	0	0
Ending balance: collectively evaluated for impairment	17,958	22,851	17,958	22,851	21,284
Unallocated
Allowance for loan losses:
Beginning Balance	1,244	585	791	642
Provision charged to expense	87	232	540	175
Losses charged off	0	0	0	0
Recoveries	0	0	0	0
Ending Balance	1,331	817	1,331	817
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	1,331	817	1,331	817	791
Loans:
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	$ 0	$ 0	$ 0	$ 0	$ 0