Loans and Allowance for Loan Losses - Summary of Additional Information Pertaining to the Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for impaired loans	$ 149	$ 133
Allowance for non-impaired loans	6,414	6,651
Total allowance for loan losses	6,563	6,784	$ 4,996	$ 4,280
Impaired loans	10,047	8,949
Non-impaired loans	487,714	480,356
Total loans	497,761	489,305
Commercial Real Estate Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for impaired loans	17
Allowance for non-impaired loans	3,373	3,402
Total allowance for loan losses	3,390	3,402	2,241	1,840
Impaired loans	5,779	4,751
Non-impaired loans	141,151	139,142
Total loans	146,930	143,893
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for non-impaired loans	401	416
Total allowance for loan losses	401	416	280	235
Non-impaired loans	23,869	20,259
Total loans	23,869	20,259
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for non-impaired loans	105	127
Total allowance for loan losses	105	127	137	128
Non-impaired loans	8,724	10,289
Total loans	8,724	10,289
One-to-Four Family [Member] | Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for impaired loans	132	133
Allowance for non-impaired loans	1,390	1,513
Total allowance for loan losses	1,522	1,646	1,223	1,096
Impaired loans	3,845	3,575
Non-impaired loans	235,345	232,073
Total loans	239,190	235,648
Second Mortgages and HELOC [Member] | Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for non-impaired loans	425	442
Total allowance for loan losses	425	442	343	289
Impaired loans	423	623
Non-impaired loans	48,650	47,543
Total loans	49,073	48,166
Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for non-impaired loans	720	751
Total allowance for loan losses	720	751	$ 772	$ 692
Non-impaired loans	29,975	31,050
Total loans	$ 29,975	$ 31,050