Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 930	$ 276
With no required reserve recorded, Unpaid Balance Principal	1,165	503
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	583	295
With no required reserve recorded, Interest Income	6	5
With required reserve recorded, Carrying Value	2,322	2,775
With required reserve recorded, Unpaid Balance Principal	2,443	2,890
With required reserve recorded, Required Reserve	102	145
With required reserve recorded, Average Carrying Value Recognized	2,578	5,196
With required reserve recorded, Interest Income	97	191
Carrying Value	3,252	3,051	$ 7,114
Unpaid Balance Principal	3,608	3,393
With required reserve recorded, Required Reserve	102	145
Average Carrying Value Recognized	3,161	5,491	$ 5,608
Interest Income	103	196
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	770	87
With no required reserve recorded, Unpaid Balance Principal	976	291
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	138	46
With no required reserve recorded, Interest Income	6	5
With required reserve recorded, Carrying Value	136	314
With required reserve recorded, Unpaid Balance Principal	137	315
With required reserve recorded, Required Reserve	15	54
With required reserve recorded, Average Carrying Value Recognized	264	462
With required reserve recorded, Interest Income	7	13
Carrying Value	906	401
Unpaid Balance Principal	1,113	606
With required reserve recorded, Required Reserve	15	54
Average Carrying Value Recognized	402	508
Interest Income	13	18
Municipal [Member] | Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	160	189
With no required reserve recorded, Unpaid Balance Principal	189	212
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	445	249
With required reserve recorded, Carrying Value	2,186	2,461
With required reserve recorded, Unpaid Balance Principal	2,306	2,575
With required reserve recorded, Required Reserve	87	91
With required reserve recorded, Average Carrying Value Recognized	2,314	2,322
With required reserve recorded, Interest Income	90	97
Carrying Value	2,346	2,650
Unpaid Balance Principal	2,495	2,787
With required reserve recorded, Required Reserve	87	91
Average Carrying Value Recognized	2,759	2,571
Interest Income	90	97
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
With required reserve recorded, Average Carrying Value Recognized		2,412
With required reserve recorded, Interest Income		81
Average Carrying Value Recognized		2,412
Interest Income		81
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