Retirement Plan and Other Post-Retirement Benefits - Schedule of Fair Value of Plan Assets (Details) - USD ($) $ in Thousands		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Miscellaneous Accruals, Interest Receivables, and Non-Interest Cash		$ (7,390)	$ (9,985)
Total plan assets		778,117	823,985	$ 784,712	$ 845,205
Retirement Plan | Total Retirement Plan Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		871,600	917,652
Retirement Plan | Domestic Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[1]	116	37,984
Retirement Plan | Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[2]	79,470	38,234
Retirement Plan | Domestic Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[3],[4]	645,955	681,755
Retirement Plan | Domestic Fixed Income | Derivative
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		6,200	8,500
Retirement Plan | International Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[5]	9,609	8,587
Retirement Plan | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[6]	102,373	109,383
Retirement Plan | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		34,077	41,709
Retirement Plan | Total Retirement Plan Investments (excluding 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		785,507	833,970
Retirement Plan | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		86,093	83,682
Other Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Miscellaneous Accruals, Interest Receivables, and Non-Interest Cash		(285)	1,243
Total plan assets		496,106	496,065	$ 455,702	$ 461,438
Other Post-Retirement Benefits | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		12,302	14,274
Other Post-Retirement Benefits | Total Investments (including 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		496,391	494,822
Other Post-Retirement Benefits | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		86,093	83,682
Other Post-Retirement Benefits | Total VEBA Trust Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		410,298	411,140
Other Post-Retirement Benefits | Collective Trust Funds — Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		232,395	82,814
Other Post-Retirement Benefits | Exchange Traded Funds — Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		165,601	314,052
Level 1 | Retirement Plan | Total Retirement Plan Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		116	37,984
Level 1 | Retirement Plan | Domestic Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[1]	116	37,984
Level 1 | Retirement Plan | Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[2]	0	0
Level 1 | Retirement Plan | Domestic Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[3],[4]	0	0
Level 1 | Retirement Plan | International Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[5]	0	0
Level 1 | Retirement Plan | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[6]	0	0
Level 1 | Retirement Plan | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 1 | Retirement Plan | Total Retirement Plan Investments (excluding 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		104	34,484
Level 1 | Retirement Plan | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		12	3,500
Level 1 | Other Post-Retirement Benefits | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 1 | Other Post-Retirement Benefits | Total Investments (including 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		165,613	317,552
Level 1 | Other Post-Retirement Benefits | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		12	3,500
Level 1 | Other Post-Retirement Benefits | Total VEBA Trust Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		165,601	314,052
Level 1 | Other Post-Retirement Benefits | Collective Trust Funds — Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 1 | Other Post-Retirement Benefits | Exchange Traded Funds — Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		165,601	314,052
Level 2 | Retirement Plan | Total Retirement Plan Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		606,514	642,187
Level 2 | Retirement Plan | Domestic Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[1]	0	0
Level 2 | Retirement Plan | Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[2]	0	0
Level 2 | Retirement Plan | Domestic Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[3],[4]	596,905	633,600
Level 2 | Retirement Plan | International Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[5]	9,609	8,587
Level 2 | Retirement Plan | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[6]	0	0
Level 2 | Retirement Plan | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 2 | Retirement Plan | Total Retirement Plan Investments (excluding 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		546,135	583,021
Level 2 | Retirement Plan | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		60,379	59,166
Level 2 | Other Post-Retirement Benefits | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 2 | Other Post-Retirement Benefits | Total Investments (including 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		60,379	59,166
Level 2 | Other Post-Retirement Benefits | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		60,379	59,166
Level 2 | Other Post-Retirement Benefits | Total VEBA Trust Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 2 | Other Post-Retirement Benefits | Collective Trust Funds — Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 2 | Other Post-Retirement Benefits | Exchange Traded Funds — Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Retirement Plan | Total Retirement Plan Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Retirement Plan | Domestic Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[1]	0	0
Level 3 | Retirement Plan | Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[2]	0	0
Level 3 | Retirement Plan | Domestic Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[3],[4]	0	0
Level 3 | Retirement Plan | International Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[5]	0	0
Level 3 | Retirement Plan | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[6]	0	0
Level 3 | Retirement Plan | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Retirement Plan | Total Retirement Plan Investments (excluding 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Retirement Plan | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Other Post-Retirement Benefits | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Other Post-Retirement Benefits | Total Investments (including 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Other Post-Retirement Benefits | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Other Post-Retirement Benefits | Total VEBA Trust Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Other Post-Retirement Benefits | Collective Trust Funds — Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Level 3 | Other Post-Retirement Benefits | Exchange Traded Funds — Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals		0	0
Measured at NAV | Retirement Plan | Total Retirement Plan Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	264,970	237,481
Measured at NAV | Retirement Plan | Domestic Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[1],[7]	0	0
Measured at NAV | Retirement Plan | Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[2],[7]	79,470	38,234
Measured at NAV | Retirement Plan | Domestic Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[3],[4],[7]	49,050	48,155
Measured at NAV | Retirement Plan | International Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[5],[7]	0	0
Measured at NAV | Retirement Plan | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[6],[7]	102,373	109,383
Measured at NAV | Retirement Plan | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	34,077	41,709
Measured at NAV | Retirement Plan | Total Retirement Plan Investments (excluding 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	239,268	216,465
Measured at NAV | Retirement Plan | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	25,702	21,016
Measured at NAV | Other Post-Retirement Benefits | Cash Held in Collective Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	12,302	14,274
Measured at NAV | Other Post-Retirement Benefits | Total Investments (including 401(h) Investments)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	270,399	118,104
Measured at NAV | Other Post-Retirement Benefits | 401(h) Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	25,702	21,016
Measured at NAV | Other Post-Retirement Benefits | Total VEBA Trust Investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	244,697	97,088
Measured at NAV | Other Post-Retirement Benefits | Collective Trust Funds — Global Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	232,395	82,814
Measured at NAV | Other Post-Retirement Benefits | Exchange Traded Funds — Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, subtotals	[7]	$ 0	$ 0

[1] Domestic Equities include mostly collective trust funds, common stock, and exchange traded funds.

[2] Global Equities are comprised of collective trust funds.

[3] Domestic Fixed Income securities include $6.2 million and $8.5 million of derivative instruments used as part of the Company’s overall liability-driven investment strategy as a way to assist in matching the duration of the assets of the Retirement Plan investments with its liability to plan participants as of September 30, 2025 and September 30, 2024, respectively.

[4] Domestic Fixed Income securities include mostly collective trust funds, corporate/government bonds and mortgages, and exchange traded funds.

[5] International Fixed Income securities are comprised mostly of corporate/government bonds.

[6] Real Estate consists of investments held in a collective trust fund and a partnership.

[7] Reflects the authoritative guidance related to investments measured at net asset value (NAV).