Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 254	$ 280	$ 254	$ 280
With no required reserve recorded, Unpaid Balance Principal	500	501	500	501
With no required reserve recorded, Average Carrying Value Recognized	818	336	616	314
With no required reserve recorded, Interest Income	2		6
With required reserve recorded, Carrying Value	2,322	5,735	2,322	5,735
With required reserve recorded, Unpaid Balance Principal	2,442	5,865	2,442	5,865
With required reserve recorded, Required Reserve	88	538	88	538
With required reserve recorded, Average Carrying Value Recognized	2,450	5,526	2,649	5,904
With required reserve recorded, Interest Income	25	29	73	165
Carrying Value	2,576	6,015	2,576	6,015
Unpaid Balance Principal	2,942	6,366	2,942	6,366
With required reserve recorded, Required Reserve	88	538	88	538
Average Carrying Value Recognized	3,268		3,265	6,218
Interest Income	27	29	79	165
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value		84		84
With no required reserve recorded, Unpaid Balance Principal		282		282
With no required reserve recorded, Average Carrying Value Recognized		56		47
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	87		87
With no required reserve recorded, Unpaid Balance Principal	306		306
With no required reserve recorded, Average Carrying Value Recognized	89		87
With no required reserve recorded, Interest Income	2		6
With required reserve recorded, Carrying Value	116	576	116	576
With required reserve recorded, Unpaid Balance Principal	116	593	116	593
With required reserve recorded, Required Reserve	2	93	2	93
With required reserve recorded, Average Carrying Value Recognized	310	589	299	490
With required reserve recorded, Interest Income	2	5	6	14
Carrying Value	203	660	203	660
Unpaid Balance Principal	422	875	422	875
With required reserve recorded, Required Reserve	2	93	2	93
Average Carrying Value Recognized		645	386	537
Interest Income	4	5	12	14
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Average Carrying Value Recognized	399
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	167	196	167	196
With no required reserve recorded, Unpaid Balance Principal	194	219	194	219
With no required reserve recorded, Average Carrying Value Recognized	729	280	529	267
With required reserve recorded, Carrying Value	2,206	2,484	2,206	2,484
With required reserve recorded, Unpaid Balance Principal	2,326	2,597	2,326	2,597
With required reserve recorded, Required Reserve	86	95	86	95
With required reserve recorded, Average Carrying Value Recognized	2,140	2,262	2,350	2,278
With required reserve recorded, Interest Income	23	24	67	71
Carrying Value	2,373	2,680	2,373	2,680
Unpaid Balance Principal	2,520	2,816	2,520	2,816
With required reserve recorded, Required Reserve	86	95	86	95
Average Carrying Value Recognized	2,869	2,542	2,879	2,545
Interest Income	$ 23	24	$ 67	71
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With required reserve recorded, Carrying Value		2,675		2,675
With required reserve recorded, Unpaid Balance Principal		2,675		2,675
With required reserve recorded, Required Reserve		350		350
With required reserve recorded, Average Carrying Value Recognized		2,675		3,136
With required reserve recorded, Interest Income				80
Carrying Value		2,675		2,675
Unpaid Balance Principal		2,675		2,675
With required reserve recorded, Required Reserve		350		350
Average Carrying Value Recognized		2,675		3,136
Interest Income				$ 80
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Average Carrying Value Recognized		$ 5,862