Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 918	$ 131	$ 918	$ 131
With no required reserve recorded, Unpaid Principal Balance	1,193	216	1,193	216
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	746	149	470	360
With no required reserve recorded, Interest Income	13	2	43	6
With required reserve recorded, Carrying Value	3,491	3,218	3,491	3,218
With required reserve recorded, Unpaid Principal Balance	3,624	3,525	3,624	3,525
With required reserve recorded, Required Reserve	163	261	163	261
With required reserve recorded, Average Carrying Value Recognized	3,688	3,254	3,138	4,489
With required reserve recorded, Interest Income	34	20	75	71
Carrying Value	4,409	3,349	4,409	3,349
Unpaid Principal Balance	4,817	3,741	4,817	3,741
With required reserve recorded, Required Reserve	163	261	163	261
Average Carrying Value Recognized	4,434	3,403	3,608	4,849
Interest Income	47	22	118	77
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0	0	0
With required reserve recorded, Carrying Value	95	100	95	100
With required reserve recorded, Unpaid Principal Balance	108	108	108	108
With required reserve recorded, Required Reserve	4	11	4	11
With required reserve recorded, Average Carrying Value Recognized	96	101	97	102
Carrying Value	95	100	95	100
Unpaid Principal Balance	108	108	108	108
With required reserve recorded, Required Reserve	4	11	4	11
Average Carrying Value Recognized	96	101	97	102
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	228	12	228	12
With no required reserve recorded, Unpaid Principal Balance	414	12	414	12
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	51	27	54	36
With no required reserve recorded, Interest Income	2		7
With required reserve recorded, Carrying Value	171	527	171	527
With required reserve recorded, Unpaid Principal Balance	187	728	187	728
With required reserve recorded, Required Reserve	9	25	9	25
With required reserve recorded, Average Carrying Value Recognized	353	551	367	670
With required reserve recorded, Interest Income	2	5	7	16
Carrying Value	399	539	399	539
Unpaid Principal Balance	601	740	601	740
With required reserve recorded, Required Reserve	9	25	9	25
Average Carrying Value Recognized	404	578	421	706
Interest Income	4	5	14	16
Municipal [Member] | Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0	0	0
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	593		593
With no required reserve recorded, Unpaid Principal Balance	593		593
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	594		310	196
With no required reserve recorded, Interest Income	9		30
With required reserve recorded, Carrying Value	3,114	1,692	3,114	1,692
With required reserve recorded, Unpaid Principal Balance	3,219	1,789	3,219	1,789
With required reserve recorded, Required Reserve	143	98	143	98
With required reserve recorded, Average Carrying Value Recognized	3,128	1,700	2,251	2,809
With required reserve recorded, Interest Income	31	14	64	48
Carrying Value	3,707	1,692	3,707	1,692
Unpaid Principal Balance	3,812	1,789	3,812	1,789
With required reserve recorded, Required Reserve	143	98	143	98
Average Carrying Value Recognized	3,722	1,700	2,561	3,005
Interest Income	40	14	94	48
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	97	119	97	119
With no required reserve recorded, Unpaid Principal Balance	186	204	186	204
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	101	122	106	128
With no required reserve recorded, Interest Income	2	2	6	6
With required reserve recorded, Carrying Value	111	808	111	808
With required reserve recorded, Unpaid Principal Balance	110	809	110	809
With required reserve recorded, Required Reserve	7	36	7	36
With required reserve recorded, Average Carrying Value Recognized	111	811	387	817
With required reserve recorded, Interest Income	1	1	4	7
Carrying Value	208	927	208	927
Unpaid Principal Balance	296	1,013	296	1,013
With required reserve recorded, Required Reserve	7	36	7	36
Average Carrying Value Recognized	212	933	493	945
Interest Income	3	3	10	13
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0	0	0
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	$ 0	0	0	0
With required reserve recorded, Carrying Value		91		91
With required reserve recorded, Unpaid Principal Balance		91		91
With required reserve recorded, Required Reserve		91		91
With required reserve recorded, Average Carrying Value Recognized		91	36	91
Carrying Value		91		91
Unpaid Principal Balance		91		91
With required reserve recorded, Required Reserve		91		91
Average Carrying Value Recognized		$ 91	$ 36	$ 91