Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 239	$ 895	$ 239	$ 895
With no required reserve recorded, Unpaid Balance Principal	276	948	276	948
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	286	910	275	771
With required reserve recorded, Carrying Value	2,077	2,176	2,077	2,176
With required reserve recorded, Unpaid Balance Principal	2,229	2,302	2,229	2,302
With required reserve recorded, Required Reserve	81	87	81	87
With required reserve recorded, Average Carrying Value Recognized	2,114	2,194	2,813	2,235
With required reserve recorded, Interest Income	22	22	65	68
Carrying Value	2,316	3,071	2,316	3,071
Unpaid Balance Principal	2,505	3,250	2,505	3,250
With required reserve recorded, Required Reserve	81	87	81	87
Average Carrying Value Recognized	2,400	3,104	3,088	3,006
Interest Income	22	22	65	70
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0	0	0
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value		67		67
With no required reserve recorded, Unpaid Balance Principal		88		88
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	41	73	19	288
With required reserve recorded, Carrying Value	77	93	77	93
With required reserve recorded, Unpaid Balance Principal	97	93	97	93
With required reserve recorded, Required Reserve	10	12	10	12
With required reserve recorded, Average Carrying Value Recognized	105	100	262	95
With required reserve recorded, Interest Income	1	1
Carrying Value	77	160	77	160
Unpaid Balance Principal	97	181	97	181
With required reserve recorded, Required Reserve	10	12	10	12
Average Carrying Value Recognized	146	173	281	383
Interest Income	1	1	3	5
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	239	592	239	592
With no required reserve recorded, Unpaid Balance Principal	276	624	276	624
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	245	601	256	365
With required reserve recorded, Carrying Value	2,000	2,083	2,000	2,083
With required reserve recorded, Unpaid Balance Principal	2,132	2,209	2,132	2,209
With required reserve recorded, Required Reserve	71	75	71	75
With required reserve recorded, Average Carrying Value Recognized	2,009	2,094	2,551	2,140
With required reserve recorded, Interest Income	21	21	62	65
Carrying Value	2,239	2,675	2,239	2,675
Unpaid Balance Principal	2,408	2,833	2,408	2,833
With required reserve recorded, Required Reserve	71	75	71	75
Average Carrying Value Recognized	2,254	2,695	2,807	2,505
Interest Income	21	21	62	65
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value		236		236
With no required reserve recorded, Unpaid Balance Principal		236		236
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized		236	0	118
Carrying Value		236		236
Unpaid Balance Principal		236		236
Average Carrying Value Recognized		236		118
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