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Loans and Allowance for Loan Losses - Additional Information (Detail) |  | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Sep. 30, 2020 USD ($) SecurityLoan Modification Loans | Sep. 30, 2020 USD ($) SecurityLoan Modification Loans | Dec. 31, 2019 | Jun. 30, 2020 USD ($) SecurityLoan Modification | Sep. 30, 2019 USD ($)
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Maximum amount of one-to-four family residential mortgage loans can be approved by loan officer | $ 100,000 | $ 100,000 |  |  |
Maximum amount of other secured loans real estate loans can be approved by loan officer | 50,000 | 50,000 |  |  |
Maximum amount of unsecured loans real estate loans can be approved by loan officer | 10,000 | 10,000 |  |  |
Maximum amount of one-to-four family residential mortgage loans can be approved by managing officer | 375,000 | 375,000 |  |  |
Maximum amount other secured loans residential mortgage loans can be approved by managing officer | 375,000 | 375,000 |  |  |
Maximum amount of unsecured loans residential mortgage loans can be approved by managing officer | 100,000 | 100,000 |  |  |
Maximum amount of unsecured loans real estate loans can be approved by loan committee | 500,000 | 500,000 |  |  |
Maximum aggregate loan amount of one-to four-family residential mortgage loans, commercial real estate loans, multi-family real estate loans and land loans can be approved by loan committee | 2,000,000 | 2,000,000 |  |  |
Troubled debt restructurings, Impaired loans | 1,298,000 | 1,298,000 |  | $ 1,330,000 |
Foreclosed residential real estate properties | 440,000 | 440,000 |  | 386,000 |
Residential real estate properties foreclosure proceedings | 34,000 | $ 34,000 |  |  |
Minimum period for default |  | 90 days |  |  |
Loans and Leases Receivable, Gross | 525,033,000 | $ 525,033,000 |  | 515,887,000 | $ 496,903,000
Fair Value, Concentration of Risk, Collateral Policy [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Commercial and multi-family real estate | 267,104,000 | 267,104,000 |  | $ 256,015,000 |
Troubled Debt Restructurings [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Troubled debt restructurings, Impaired loans | 1,300,000 | 1,300,000 |  |  |
Troubled Debt Restructurings [Member] | Covid Nineteen [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Investment recorded prior to modification |  | 83,100,000 |  |  |
Troubled Debt Restructurings [Member] | Covid Nineteen [Member] | Modification One [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Financing Receivable, Modifications, Post-Modification Recorded Investment | $ 26,400,000 | 26,400,000 |  |  |
Troubled Debt Restructurings [Member] | Covid Nineteen [Member] | Modification Two [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Number of Modifications | Modification | 123 |  |  |  |
Financing Receivable, Modifications, Post-Modification Recorded Investment | $ 56,700,000 | 56,700,000 |  |  |
Residential Real Estate [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Foreclosed residential real estate properties | 209,000 | 209,000 |  |  |
Commercial [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Number of Modifications | Modification |  |  |  | 1 |
Loans and Leases Receivable, Gross | 157,096,000 | 157,096,000 |  | $ 145,113,000 | 146,500,000
Commercial Business Loans [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Investment recorded prior to modification |  |  |  | 61,000 |
Loans and Leases Receivable, Gross | $ 109,182,000 | $ 109,182,000 |  | 107,581,000 | 84,825,000
Commercial Business Loans [Member] | Small Business Administration Paycheck Protection Programme Loans [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Percentage of government guarantee for loans as per scheme | 100.00% | 100.00% |  |  |
Commercial Portfolio And Commercial Residential Portfolio [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Number of loans as on closing date | Loans | 304 | 304 |  |  |
Loans and Leases Receivable, Gross | $ 26,300,000 | $ 26,300,000 |  |  |
One- to four-family [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Maximum term of fixed-rate one- to four-family residential mortgage loans |  | 15 years |  |  |
Troubled debt restructurings, Impaired loans | $ 1,243,000 | $ 1,243,000 |  | $ 1,256,000 |
Number of default loans | SecurityLoan |  | 1 |  | 1 |
Number of troubled debt restructurings in accrual status | SecurityLoan | 9 | 9 |  | 9 |
Amount of troubled debt restructurings in accrual status | $ 1,200,000 | $ 1,200,000 |  | $ 1,300,000 |
Investment recorded post modification |  | 125,000 |  | 127,000 |
Loans and Leases Receivable, Gross | 125,574,000 | $ 125,574,000 |  | $ 128,876,000 | $ 126,152,000
One- to four-family [Member] | Troubled Debt Restructurings [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Number of default loans | SecurityLoan |  | 1 |  | 1 |
Investment recorded post modification |  |  |  | $ 127,000 |
Purchased Loans and Loan Participations [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Approximate amount of purchase loans included in loans receivable | 3,895,000 | $ 3,895,000 |  | 4,181,000 |
Approximate amount of loans included on out-of-area participation | 25,354,000 | 25,354,000 |  | 23,950,000 |
Amount within 100 miles of primary area | $ 7,853,000 | $ 7,853,000 |  | $ 8,126,000 |
Troubled Debt Restructurings [Member] | Covid Nineteen [Member] | Modification One [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Number of Modifications | Modification |  | 181 |  |  |
Foreclosure [Member] | Troubled Debt Restructurings [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Number of default loans | SecurityLoan |  | 0 |  | 0 |
Investment recorded post modification default loans |  | $ 125,000 |  |  |
Non troubled debt restructuring [Member] | Covid Nineteen [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] |  |  |  |  |
Loans and Allowance for Credit Losses [Line Items] |  |  |  |  |
Financing receivable number of days past due |  |  | 30 days |  |
Period of loan execution |  |  | 60 days |  |

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