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, 2025 USD ($)	[1]
Non-Qualified Benefit Plans
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Net Actuarial Loss	$ (13,353)
Prior Service (Cost) Credit	0
Net Amount Recognized	(13,353)
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Increase in Actuarial Loss, excluding amortization	(1,061)	[2]
Change due to Amortization of Actuarial Loss	1,101
Prior Service (Cost) Credit	0
Net Change	40
Retirement Plan | Qualified Plan
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Net Actuarial Loss	(178,675)
Prior Service (Cost) Credit	(1,372)
Net Amount Recognized	(180,047)
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Increase in Actuarial Loss, excluding amortization	(20,828)	[2]
Change due to Amortization of Actuarial Loss	6,481
Prior Service (Cost) Credit	302
Net Change	(14,045)
Other Post-Retirement Benefits | Qualified Plan
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Net Actuarial Loss	(19,813)
Prior Service (Cost) Credit	257
Net Amount Recognized	(19,556)
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities
Increase in Actuarial Loss, excluding amortization	(19,722)	[2]
Change due to Amortization of Actuarial Loss	37
Prior Service (Cost) Credit	(429)
Net Change	$ (20,114)

[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.