Minimum Regulatory Capital Requirements - Summary of Bank's Actual and Required Capital Amounts and Ratios (Detail) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2019
Federal Home Loan Banks [Abstract]
Common Equity Tier 1 Capital to Risk Weighted Assets Actual, Amount	$ 164,322	$ 152,855
Total Risk-Based Capital to Risk Weighted Assets Actual, Amount	178,635	160,562
Tier 1 Capital to Risk Weighted Assets Actual, Amount	164,322	152,855
Tier 1 leverage Capital to Adjusted Total Assets Actual, Amount	$ 164,322	$ 152,855
Common Equity Tier 1 Capital to Risk Weighted Assets Actual, Ratio	11.63%	11.71%
Total Risk-Based Capital to Risk Weighted Assets Actual, Ratio	12.64	12.30
Tier 1 Capital to Risk Weighted Assets Actual, Ratio	11.63	11.71
Tier 1 leverage Capital to Adjusted Total Assets Actual, Ratio	9.08	10.02	4.0
Common Equity Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 63,542	$ 58,725
Total Risk-Based Capital to Risk Weighted Assets For Capital Adequacy Purposes, Amount	113,032	104,400
Tier 1 Capital to Risk Weighted Assets For Capital Adequacy Purposes, Amount	84,774	78,300
Tier 1 leverage Capital to Adjusted Total Assets For Capital Adequacy Purposes, Amount	$ 72,419	$ 61,050
Common Equity Tier 1 Capital to Risk Weighted Assets For Capital Adequacy Purposes, Ratio	4.50%	4.50%
Total Risk-Based Capital to Risk Weighted Assets For Capital Adequacy Purposes, Ratio	8.00	8.00	8.0
Tier 1 Capital to Risk Weighted Assets For Capital Adequacy Purposes, Ratio	6.00	6.00
Tier 1 leverage Capital to Adjusted Total Assets For Capital Adequacy Purposes, Ratio	4.00	4.00
Common Equity Tier 1 Capital to Risk Weighted Assets To Be Well Capitalized Under the Prompt Corrective Action Provisions, Amount	$ 91,783	$ 84,825
Total Risk-Based Capital to Risk Weighted Assets To Be Well Capitalized Under the Prompt Corrective Action Provisions, Amount	141,290	130,500
Tier 1 Capital to Risk Weighted Assets To Be Well Capitalized Under the Prompt Corrective Action Provisions, Amount	113,032	104,400
Tier 1 leverage Capital to Adjusted Total Assets To Be Well Capitalized Under the Prompt Corrective Action Provisions, Amount	$ 90,524	$ 76,312
Common Equity Tier 1 Capital to Risk Weighted Assets To Be Well Capitalized Under the Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Total Risk-Based Capital to Risk Weighted Assets To Be Well Capitalized Under the Prompt Corrective Action Provisions, Ratio	10.00	10.00
Tier 1 Capital to Risk Weighted Assets To Be Well Capitalized Under the Prompt Corrective Action Provisions, Ratio	8.00	8.00
Tier 1 leverage Capital to Adjusted Total Assets To Be Well Capitalized Under the Prompt Corrective Action Provisions, Ratio	5.00	5.00