Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands		Sep. 30, 2023	Sep. 30, 2022
Regulatory Assets:
Total Regulatory Assets	[1]	$ 184,796	$ 203,590
Less: Amounts Included in Other Current Assets	[1]	(36,373)	(21,358)
Regulatory Liabilities:
Total Regulatory Liabilities		808,821	842,560
Less: Amounts included in Current and Accrued Liabilities		97,124	31,712
Total Long-Term Regulatory Liabilities		711,697	810,848
Cost of Removal Regulatory Liability
Regulatory Liabilities:
Total Regulatory Liabilities		277,694	259,947
Taxes Refundable to Customers
Regulatory Liabilities:
Total Regulatory Liabilities		268,562	362,098
Post-Retirement Benefit Costs
Regulatory Liabilities:
Total Regulatory Liabilities	[2]	159,760	167,305
Less: Amounts included in Current and Accrued Liabilities		5,800	5,800
Total Long-Term Regulatory Liabilities		153,960	161,505
Pension Costs
Regulatory Liabilities:
Total Regulatory Liabilities	[3]	0	8,242
Amounts Payable to Customers
Regulatory Liabilities:
Total Regulatory Liabilities		59,019	419
Environmental Site Remediation Costs
Regulatory Liabilities:
Total Regulatory Liabilities	[3]	619	0
Other
Regulatory Liabilities:
Total Regulatory Liabilities	[4]	43,167	44,549
Total Long-Term Regulatory Liabilities		10,862	19,056
Other Accruals and Current Liabilities
Regulatory Liabilities:
Less: Amounts included in Current and Accrued Liabilities		32,305	25,493
Pension Costs
Regulatory Assets:
Total Regulatory Assets	[1],[5]	20,459	11,677
Post-Retirement Benefit Costs
Regulatory Assets:
Total Regulatory Assets	[1],[5]	2,536	6,814
Recoverable Future Taxes
Regulatory Assets:
Total Regulatory Assets	[1]	69,045	106,247
Environmental Site Remediation Costs
Regulatory Assets:
Total Regulatory Assets	[1],[5]	0	3,646
Asset Retirement Obligations
Regulatory Assets:
Total Regulatory Assets	[1],[5]	19,384	18,517
Unamortized Debt Expense
Regulatory Assets:
Total Regulatory Assets	[1]	7,240	8,884
Other
Regulatory Assets:
Total Regulatory Assets	[1],[6]	66,132	47,805
Total Long-Term Regulatory Assets		29,759	26,447
Long-Term Regulatory Assets
Regulatory Assets:
Total Long-Term Regulatory Assets	[1]	148,423	182,232
Other Current Assets
Regulatory Assets:
Less: Amounts Included in Other Current Assets		$ (36,373)	$ (21,358)

[1] The Company recovers the cost of its regulatory assets but generally does not earn a return on them. There are a few exceptions to this rule. For example, the Company does earn a return on Unrecovered Purchased Gas Costs and, in the New York jurisdiction of its Utility segment, earns a return, within certain parameters, on the excess of cumulative funding to the pension plan over the cumulative amount collected in rates.

[2] $5,800 is included in Other Accruals and Current Liabilities on the Consolidated Balance Sheets at both September 30, 2023 and 2022, since such amounts are expected to be passed back to ratepayers in the next 12 months. $153,960 and $161,505 are included in Other Regulatory Liabilities on the Consolidated Balance Sheets at September 30, 2023 and 2022, respectively.

[3] Included in Other Regulatory Liabilities on the Consolidated Balance Sheets.

[4] $32,305 and $25,493 are included in Other Accruals and Current Liabilities on the Consolidated Balance Sheets at September 30, 2023 and 2022, respectively, since such amounts are expected to be passed back to ratepayers in the next 12 months. $10,862 and $19,056 are included in Other Regulatory Liabilities on the Consolidated Balance Sheets at September 30, 2023 and 2022, respectively.

[5] Included in Other Regulatory Assets on the Consolidated Balance Sheets.

[6] $36,373 and $21,358 are included in Other Current Assets on the Consolidated Balance Sheets at September 30, 2023 and 2022, respectively, since such amounts are expected to be recovered from ratepayers in the next 12 months. $29,759 and $26,447 are included in Other Regulatory Assets on the Consolidated Balance Sheets at September 30, 2023 and 2022, respectively.