Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands		Dec. 19, 2024	Sep. 30, 2025	Sep. 30, 2024
Regulatory Assets:
Total Long-Term Regulatory Assets			$ 230,969	$ 193,710
Total Regulatory Assets			272,100	231,974
Regulatory Liabilities:
Total Long-Term Regulatory Liabilities			735,938	749,574
Total Regulatory Liabilities			757,530	821,646
Levelization deferral		$ 17,800
Uncollectible expense tracker		9,800
Property tax tracker		$ 1,100
Taxes Refundable to Customers
Regulatory Liabilities:
Total Long-Term Regulatory Liabilities			306,335	305,645
Cost of Removal Regulatory Liability
Regulatory Liabilities:
Total Long-Term Regulatory Liabilities			307,659	292,477
Post-Retirement Benefit Costs
Regulatory Liabilities:
Total Long-Term Regulatory Liabilities			108,714	135,399
Current Regulatory Liabilities			5,800	5,800
Environmental Site Remediation Costs
Regulatory Liabilities:
Total Long-Term Regulatory Liabilities			1,800	5,390
Other
Regulatory Liabilities:
Total Long-Term Regulatory Liabilities			11,430	10,663
Amounts Payable to Customers
Regulatory Liabilities:
Current Regulatory Liabilities			968	42,720
Other Current and Accrued Liabilities
Regulatory Liabilities:
Current Regulatory Liabilities			14,824	23,552
Recoverable Future Taxes
Regulatory Assets:
Total Long-Term Regulatory Assets			89,247	80,084
Unamortized Debt Expense
Regulatory Assets:
Total Long-Term Regulatory Assets			6,236	5,604
Pension Costs
Regulatory Assets:
Total Long-Term Regulatory Assets			42,602	30,259
NY Rate Case Levelization and Tracking Mechanisms
Regulatory Assets:
Total Long-Term Regulatory Assets	[1]		28,688	0
Asset Retirement Obligations
Regulatory Assets:
Total Long-Term Regulatory Assets			24,634	21,951
Post-Retirement Benefit Costs
Regulatory Assets:
Total Long-Term Regulatory Assets			13,306	7,932
System Modernization/Improvement Tracker
Regulatory Assets:
Total Long-Term Regulatory Assets			12,625	31,362
Current Regulatory Assets			14,481	15,681
Other
Regulatory Assets:
Total Long-Term Regulatory Assets			13,631	16,518
Current Regulatory Assets			20,881	22,583
Unrecovered Purchased Gas Costs
Regulatory Assets:
Current Regulatory Assets			$ 5,769	$ 0

[1] New York Rate Case Levelization and Tracking Mechanisms were approved in accordance with Distribution Corporation’s New York rate settlement on December 19, 2024, as discussed below. The mechanisms include: (a) levelization deferral of $17.8 million which relates to a volumetric surcredit within the Company’s delivery adjustment charge that minimizes customer bill impacts, (b) uncollectible expense tracker of $9.8 million, which tracks and reconciles the actual uncollectible expense to the amounts recovered in base rates and, (c) property tax tracker of $1.1 million, which represents the amount deferred between actual property taxes incurred and the level included in customer rates.