Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 560	$ 1,066
With no required reserve recorded, Unpaid Balance Principal	647	3,901
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value	521	662
With no required reserve recorded, Interest Income	9	1
With required reserve recorded, Carrying Value	5,767	6,722
With required reserve recorded, Unpaid Balance Principal	6,107	7,135
With required reserve recorded, Required Reserve	904	1,019
With required reserve recorded, Average Carrying Value	6,913	6,114
With required reserve recorded, Interest Income Recognized	135	160
Carrying Value	6,327	7,788	5,925
Unpaid Balance Principal	6,754	11,036
With required reserve recorded, Required Reserve	904	1,019
Average Carrying Value	7,434	6,776	7,043
Interest Income Recognized	144	161
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value		500
With no required reserve recorded, Unpaid Balance Principal		3,292
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value	173
With required reserve recorded, Carrying Value	103	108
With required reserve recorded, Unpaid Balance Principal	108	108
With required reserve recorded, Required Reserve	21	12
With required reserve recorded, Average Carrying Value	222	1,371
With required reserve recorded, Interest Income Recognized		1
Carrying Value	103	608
Unpaid Balance Principal	108	3,400
With required reserve recorded, Required Reserve	21	12
Average Carrying Value	395	1,371
Interest Income Recognized		1
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	31	238
With no required reserve recorded, Unpaid Balance Principal	32	268
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value	46	361
With no required reserve recorded, Interest Income		1
With required reserve recorded, Carrying Value	822	1,129
With required reserve recorded, Unpaid Balance Principal	1,063	1,371
With required reserve recorded, Required Reserve	57	367
With required reserve recorded, Average Carrying Value	1,065	902
With required reserve recorded, Interest Income Recognized	31	37
Carrying Value	853	1,367
Unpaid Balance Principal	1,095	1,639
With required reserve recorded, Required Reserve	57	367
Average Carrying Value	1,111	1,263
Interest Income Recognized	31	38
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	393	82
With no required reserve recorded, Unpaid Balance Principal	396	82
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value	225	132
With required reserve recorded, Carrying Value	3,924	4,438
With required reserve recorded, Unpaid Balance Principal	4,018	4,527
With required reserve recorded, Required Reserve	639	417
With required reserve recorded, Average Carrying Value	4,325	2,868
With required reserve recorded, Interest Income Recognized	103	120
Carrying Value	4,317	4,520
Unpaid Balance Principal	4,414	4,609
With required reserve recorded, Required Reserve	639	417
Average Carrying Value	4,550	3,000
Interest Income Recognized	103	120
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	136	246
With no required reserve recorded, Unpaid Balance Principal	219	259
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value	77	169
With no required reserve recorded, Interest Income	9
With required reserve recorded, Carrying Value	826	953
With required reserve recorded, Unpaid Balance Principal	826	1,035
With required reserve recorded, Required Reserve	95	129
With required reserve recorded, Average Carrying Value	1,208	878
With required reserve recorded, Interest Income Recognized	1	2
Carrying Value	962	1,199
Unpaid Balance Principal	1,045	1,294
With required reserve recorded, Required Reserve	95	129
Average Carrying Value	1,285	1,047
Interest Income Recognized	10	2
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
With required reserve recorded, Carrying Value	92	94
With required reserve recorded, Unpaid Balance Principal	92	94
With required reserve recorded, Required Reserve	92	94
With required reserve recorded, Average Carrying Value	93	95
Carrying Value	92	94
Unpaid Balance Principal	92	94
With required reserve recorded, Required Reserve	92	94
Average Carrying Value	$ 93	$ 95