Employee Stock Ownership and 401(k) Plan: Narrative (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 1998 USD ($) shares	Sep. 30, 2023 USD ($) component shares	Sep. 30, 2022 USD ($) shares	Sep. 30, 2021 USD ($) shares
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
ESOP shares (in shares) | shares		317,094	372,559	397,626
401(k)
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
401(k), employer safe harbor contribution (as a percent)		3.00%
401(k), employer contributions | $		$ 1,039,000	$ 942,000	$ 931,000
KSOP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Number of components in KSOP | component		2
Required service period (in years)		1 year
Employee minimum age requirement (in years)		18 years
Award vesting period (in years)		6 years
ESOP
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
ESOP, loan borrowed from employer | $	$ 7,930,000
ESOP, shares purchased for plan (in shares) | shares	1,058,000
ESOP, shares distributed to participants (in shares) | shares		740,906
Earned ESOP shares | $		$ 0	$ 0