Retirement Plan and Other Post-Retirement Benefits - Schedule of Cumulative Amounts Recognized in AOCI (Loss) and Regulatory Assets and Liabilities (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2024 USD ($)	[1]
Non-Qualified Benefit Plans
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Net Actuarial Loss	$ (13,394)
Prior Service (Cost) Credit	0
Net Amount Recognized	(13,394)
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Increase in Actuarial Loss, excluding amortization	(880)	[2]
Change due to Amortization of Actuarial (Gain) Loss	4,772
Prior Service (Cost) Credit	0
Net Change	3,892
Retirement Plan | Qualified Plan
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Net Actuarial Loss	(164,328)
Prior Service (Cost) Credit	(1,674)
Net Amount Recognized	(166,002)
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Increase in Actuarial Loss, excluding amortization	(34,871)	[2]
Change due to Amortization of Actuarial (Gain) Loss	(1,339)
Prior Service (Cost) Credit	362
Net Change	(35,848)
Other Post-Retirement Benefits | Qualified Plan
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Net Actuarial Loss	(128)
Prior Service (Cost) Credit	686
Net Amount Recognized	558
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Increase in Actuarial Loss, excluding amortization	(16,302)	[2]
Change due to Amortization of Actuarial (Gain) Loss	(2,266)
Prior Service (Cost) Credit	(429)
Net Change	$ (18,997)

[1] Amounts presented are shown before recognizing deferred taxes.

[2] Amounts presented include the impact of actuarial gains/losses related to return on assets, as well as the Actuarial Loss amounts presented in the Change in Benefit Obligation.