Allowance for Loan Losses and Recorded Investment in Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Allowance for loan losses:
Beginning Balance	$ 2,506	$ 3,038	$ 2,400	$ 2,894
Provision charged to expense	145	216	261	432
Losses charged off	(40)	(155)	(93)	(274)
Recoveries	86	33	129	80
Ending Balance	2,697	3,132	2,697	3,132
Ending balance: individually evaluated for impairment	463	1,676	463	1,676	$ 714
Ending balance: collectively evaluated for impairment	2,234	1,456	2,234	1,456	1,686
Loans:
Ending balance: individually evaluated for impairment	2,045	6,658	2,045	6,658	1,868
Ending balance: collectively evaluated for impairment	309,877	308,739	309,877	308,739	313,886
Commercial
Allowance for loan losses:
Beginning Balance	238	1,054	254	412
Provision charged to expense	(11)	(570)	(46)	83
Losses charged off	0	(13)	0	(25)
Recoveries	7	1	26	2
Ending Balance	234	472	234	472
Ending balance: individually evaluated for impairment	86	323	86	323	92
Ending balance: collectively evaluated for impairment	148	149	148	149	162
Loans:
Ending balance: individually evaluated for impairment	98	515	98	515	112
Ending balance: collectively evaluated for impairment	57,380	48,394	57,380	48,394	52,174
Commercial Real Estate
Allowance for loan losses:
Beginning Balance	1,119	1,080	1,116	1,609
Provision charged to expense	(351)	749	(352)	216
Losses charged off	0	0	0	0
Recoveries	3	9	7	13
Ending Balance	771	1,838	771	1,838
Ending balance: individually evaluated for impairment	377	1,353	377	1,353	622
Ending balance: collectively evaluated for impairment	394	485	394	485	494
Loans:
Ending balance: individually evaluated for impairment	1,947	6,143	1,947	6,143	1,756
Ending balance: collectively evaluated for impairment	150,317	153,047	150,317	153,047	156,558
Installment
Allowance for loan losses:
Beginning Balance	91	237	92	141
Provision charged to expense	71	(31)	66	121
Losses charged off	0	(81)	0	(178)
Recoveries	10	21	14	62
Ending Balance	172	146	172	146
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	172	146	172	146	147
Loans:
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	19,323	24,135	19,323	24,135	21,284
Residential
Allowance for loan losses:
Beginning Balance	171	90	147	90
Provision charged to expense	79	60	140	69
Losses charged off	(40)	(61)	(93)	(71)
Recoveries	66	2	82	3
Ending Balance	276	91	276	91
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	276	91	276	91	92
Loans:
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	82,857	83,163	82,857	83,163	83,870
Unallocated
Allowance for loan losses:
Beginning Balance	887	577	791	642
Provision charged to expense	357	8	453	(57)
Losses charged off	0	0	0	0
Recoveries	0	0	0	0
Ending Balance	1,244	585	1,244	585
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	1,244	585	1,244	585	791
Loans:
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	$ 0	$ 0	$ 0	$ 0	$ 0