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Fair Value Measurements - Additional Information (Details) - USD ($) | 9 Months Ended |
--- | --- | ---
Jun. 30, 2022 | Jun. 30, 2021 | Sep. 30, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Available-for-sale securities purchased | $ 516,163,000 | $ 528,937,000 |
Proceeds from sales of available-for-sale securities | 4,510,000 | 0 |
Held-to-maturity securities purchased | 195,358,000 | 0 |
Proceeds from sale of held-to-maturity securities | $ 0 | $ 0 |
Term of contractual due dates of substantially all mortgage-backed securities (in years) | 10 years |  |
Accrued interest for available-for-sale securities | $ 5,579,000 |  | $ 3,458,000
Accrued interest for held-to-maturity securities | 1,143,000 |  | $ 944,000
Consumer loans | Single-family residential |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Foreclosed residential real estate properties held as REO | 234,000 |  |
Real estate acquired through foreclosure | $ 2,313,000 |  |

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- Definition Amount, after allowance for credit loss, of accrued interest on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 3A -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL120267853-210455 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2A -URI https://asc.fasb.org/extlink&oid=126970911&loc=SL121698322-111563 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 3B -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL120267856-210455 + Details
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- Definition Amount, after allowance for credit loss, of accrued interest on investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5C -URI https://asc.fasb.org/extlink&oid=126970911&loc=SL121698325-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 5 -URI https://asc.fasb.org/extlink&oid=124255206&loc=SL120267845-210446 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3A -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL120267960-210447 + Details
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- Definition Carrying amount of other real estate not separately disclosed, including, but not limited to, real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. This does not include real estate assets taken in settlement of troubled loans through surrender or foreclosure. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.10(4)) -URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878 + Details
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