Allowance for Loan Losses and Recorded Investment in Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Allowance for loan losses:
Balance, beginning of period	$ 2,375	$ 2,506	$ 2,437	$ 2,400
Provision charged to expense	105	145	176	261
Losses charged off	(120)	(40)	(284)	(93)
Recoveries	105	86	136	129
Balance, end of period	2,465	2,697	2,465	2,697
Ending balance: individually evaluated for impairment	278	463	278	463	$ 181
Ending balance: collectively evaluated for impairment	2,187	2,234	2,187	2,234	2,256
Loans:
Ending balance: individually evaluated for impairment	1,369	2,045	1,369	2,045	1,410
Ending balance: collectively evaluated for impairment	348,822	309,877	348,822	309,877	328,253
Commercial
Allowance for loan losses:
Balance, beginning of period	192	238	184	254
Provision charged to expense	231	(11)	238	(46)
Losses charged off	0	0	(2)	0
Recoveries	74	7	77	26
Balance, end of period	497	234	497	234
Ending balance: individually evaluated for impairment	0	86	0	86	9
Ending balance: collectively evaluated for impairment	497	148	497	148	175
Loans:
Ending balance: individually evaluated for impairment	1	98	1	98	57
Ending balance: collectively evaluated for impairment	86,538	57,380	86,538	57,380	67,190
Commercial Real Estate
Allowance for loan losses:
Balance, beginning of period	702	1,119	597	1,116
Provision charged to expense	(278)	(351)	(177)	(352)
Losses charged off	0	0	0	0
Recoveries	3	3	7	7
Balance, end of period	427	771	427	771
Ending balance: individually evaluated for impairment	278	377	278	377	172
Ending balance: collectively evaluated for impairment	149	394	149	394	425
Loans:
Ending balance: individually evaluated for impairment	1,368	1,947	1,368	1,947	1,273
Ending balance: collectively evaluated for impairment	167,149	150,317	167,149	150,317	162,186
Residential
Allowance for loan losses:
Balance, beginning of period	166	171	170	147
Provision charged to expense	(15)	79	72	140
Losses charged off	0	(40)	(91)	(93)
Recoveries	12	66	12	82
Balance, end of period	163	276	163	276
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	163	276	163	276	170
Loans:
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	78,307	82,857	78,307	82,857	81,498
Installment
Allowance for loan losses:
Balance, beginning of period	236	91	113	92
Provision charged to expense	9	71	179	66
Losses charged off	(120)	0	(191)	0
Recoveries	16	10	40	14
Balance, end of period	141	172	141	172
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	141	172	141	172	113
Loans:
Ending balance: individually evaluated for impairment	0	0	0	0	80
Ending balance: collectively evaluated for impairment	15,459	19,323	15,459	19,323	17,379
Unallocated
Allowance for loan losses:
Balance, beginning of period	1,079	887	1,373	791
Provision charged to expense	158	357	(136)	453
Losses charged off	0	0	0	0
Recoveries	0	0	0	0
Balance, end of period	1,237	1,244	1,237	1,244
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	1,237	1,244	1,237	1,244	1,373
Loans:
Ending balance: individually evaluated for impairment	0	0	0	0	0
Ending balance: collectively evaluated for impairment	$ 0	$ 0	$ 0	$ 0	$ 0