Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands		Sep. 30, 2024	Sep. 30, 2023
Regulatory Assets:
Total Regulatory Assets		$ 231,974	$ 184,796
Less: Amounts Included in Other Current Assets		(38,264)	(36,373)
Regulatory Liabilities:
Total Regulatory Liabilities		821,646	808,821
Less: Amounts included in Current and Accrued Liabilities		(72,072)	(97,124)
Total Long-Term Regulatory Liabilities		749,574	711,697
Cost of Removal Regulatory Liability
Regulatory Liabilities:
Total Regulatory Liabilities		292,477	277,694
Taxes Refundable to Customers
Regulatory Liabilities:
Total Regulatory Liabilities		305,645	268,562
Post-Retirement Benefit Costs
Regulatory Liabilities:
Total Regulatory Liabilities	[1]	141,199	159,760
Less: Amounts included in Current and Accrued Liabilities		(5,800)	(5,800)
Total Long-Term Regulatory Liabilities		135,399	153,960
Amounts Payable to Customers
Regulatory Liabilities:
Total Regulatory Liabilities		42,720	59,019
Environmental Site Remediation Costs
Regulatory Liabilities:
Total Regulatory Liabilities	[2]	5,390	619
Other
Regulatory Liabilities:
Total Regulatory Liabilities	[3]	34,215	43,167
Total Long-Term Regulatory Liabilities		10,663	10,862
Other Accruals and Current Liabilities
Regulatory Liabilities:
Less: Amounts included in Current and Accrued Liabilities		(23,552)	(32,305)
Pension Costs
Regulatory Assets:
Total Regulatory Assets	[4]	30,259	20,459
Post-Retirement Benefit Costs
Regulatory Assets:
Total Regulatory Assets	[4]	7,932	2,536
Recoverable Future Taxes
Regulatory Assets:
Total Regulatory Assets		80,084	69,045
System Modernization And Improvement Tracker
Regulatory Assets:
Total Regulatory Assets	[5]	47,043	30,375
Less: Amounts Included in Other Current Assets		(15,681)	(19,584)
Total Long-Term Regulatory Assets		31,362	10,791
Asset Retirement Obligations
Regulatory Assets:
Total Regulatory Assets	[4]	21,951	19,384
Unamortized Debt Expense
Regulatory Assets:
Total Regulatory Assets		5,604	7,240
Other
Regulatory Assets:
Total Regulatory Assets	[6]	39,101	35,757
Total Long-Term Regulatory Assets		16,518	18,968
Long-Term Regulatory Assets
Regulatory Assets:
Total Long-Term Regulatory Assets		193,710	148,423
Other Current Assets
Regulatory Assets:
Less: Amounts Included in Other Current Assets		$ (22,583)	$ (16,789)

[1] $5,800 is included in Other Accruals and Current Liabilities on the Consolidated Balance Sheets at both September 30, 2024 and 2023, since such amounts are expected to be passed back to ratepayers in the next 12 months. $135,399 and $153,960 are included in Other Regulatory Liabilities on the Consolidated Balance Sheets at September 30, 2024 and 2023, respectively.

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

[3] $23,552 and $32,305 are included in Other Accruals and Current Liabilities on the Consolidated Balance Sheets at September 30, 2024 and 2023, respectively, since such amounts are expected to be passed back to ratepayers in the next 12 months. $10,663 and $10,862 are included in Other Regulatory Liabilities on the Consolidated Balance Sheets at September 30, 2024 and 2023, respectively.

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

[5] $15,681 and $19,584 are included in Other Current Assets on the Consolidated Balance Sheets at September 30, 2024 and 2023, respectively, since such amounts are expected to be recovered from ratepayers in the next 12 months. $31,362 and $10,791 are included in Other Regulatory Assets on the Consolidated Balance Sheets at September 30, 2024 and 2023, respectively.

[6] $22,583 and $16,789 are included in Other Current Assets on the Consolidated Balance Sheets at September 30, 2024 and 2023, respectively, since such amounts are expected to be recovered from ratepayers in the next 12 months. $16,518 and $18,968 are included in Other Regulatory Assets on the Consolidated Balance Sheets at September 30, 2024 and 2023, respectively.