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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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