v3.26.1
Fair Value Measurements (Schedule of Recurring Fair Value Measures of Assets and Liabilities) (Details) - Fair Value, Recurring - USD ($)
$ in Thousands
Mar. 31, 2026
Sep. 30, 2025
Derivative Financial Instruments:    
Derivative Asset Netting Adjustment [1] $ (37,033) $ (47,095)
Derivative Asset, Statement of Financial Position [Extensible Enumeration] Fair Value of Derivative Financial Instruments Fair Value of Derivative Financial Instruments
Total Assets [1] $ 160,452 $ 93,807
Derivative Financial Instruments:    
Derivative Liability Netting Adjustments [1] $ (37,033) $ (47,095)
Derivative Liability, Statement of Financial Position [Extensible Enumeration] Fair Value of Derivative Financial Instruments Fair Value of Derivative Financial Instruments
Total Liabilities [1] $ 236 $ 6,003
Total Net Assets/(Liabilities) Netting Adjustments [1] 0 0
Total Net Assets/(Liabilities) [1] 160,216 87,804
Money Market Funds    
Assets:    
Cash Equivalents – Money Market Mutual Funds [1] 20,340 30,551
Over the Counter Swaps — Gas    
Derivative Financial Instruments:    
Derivative Asset Netting Adjustment [1] (33,832) (33,615)
Derivative asset [1] 89,865 28,575
Derivative Financial Instruments:    
Derivative Liability Netting Adjustments [1] (33,832) (33,615)
Derivative liability [1] 0 554
Over the Counter No Cost Collars – Gas    
Derivative Financial Instruments:    
Derivative Asset Netting Adjustment [1] (2,548) (12,805)
Derivative asset [1] 26,709 11,344
Derivative Financial Instruments:    
Derivative Liability Netting Adjustments [1] (2,548) (12,805)
Derivative liability [1] 0 5,231
Foreign Currency Contracts    
Derivative Financial Instruments:    
Derivative Asset Netting Adjustment [1] (653) (675)
Derivative asset [1] (560) (531)
Derivative Financial Instruments:    
Derivative Liability Netting Adjustments [1] (653) (675)
Derivative liability [1] 236 218
Balanced Equity Mutual Fund    
Derivative Financial Instruments:    
Other Investments [1] 13,872 13,786
Fixed Income Mutual Fund    
Derivative Financial Instruments:    
Other Investments [1] 10,226 10,082
Level 1    
Derivative Financial Instruments:    
Total Assets 44,438 54,419
Derivative Financial Instruments:    
Total Liabilities 0 0
Total Net Assets/(Liabilities) 44,438 54,419
Level 1 | Money Market Funds    
Assets:    
Cash Equivalents – Money Market Mutual Funds 20,340 30,551
Level 1 | Over the Counter Swaps — Gas    
Derivative Financial Instruments:    
Derivative Asset 0 0
Derivative Financial Instruments:    
Derivative Liability 0 0
Level 1 | Over the Counter No Cost Collars – Gas    
Derivative Financial Instruments:    
Derivative Asset 0 0
Derivative Financial Instruments:    
Derivative Liability 0 0
Level 1 | Foreign Currency Contracts    
Derivative Financial Instruments:    
Derivative Asset 0 0
Derivative Financial Instruments:    
Derivative Liability 0 0
Level 1 | Balanced Equity Mutual Fund    
Derivative Financial Instruments:    
Other Investments 13,872 13,786
Level 1 | Fixed Income Mutual Fund    
Derivative Financial Instruments:    
Other Investments 10,226 10,082
Level 2    
Derivative Financial Instruments:    
Total Assets 153,047 86,483
Derivative Financial Instruments:    
Total Liabilities 37,269 53,098
Total Net Assets/(Liabilities) 115,778 33,385
Level 2 | Money Market Funds    
Assets:    
Cash Equivalents – Money Market Mutual Funds 0 0
Level 2 | Over the Counter Swaps — Gas    
Derivative Financial Instruments:    
Derivative Asset 123,697 62,190
Derivative Financial Instruments:    
Derivative Liability 33,832 34,169
Level 2 | Over the Counter No Cost Collars – Gas    
Derivative Financial Instruments:    
Derivative Asset 29,257 24,149
Derivative Financial Instruments:    
Derivative Liability 2,548 18,036
Level 2 | Foreign Currency Contracts    
Derivative Financial Instruments:    
Derivative Asset 93 144
Derivative Financial Instruments:    
Derivative Liability 889 893
Level 2 | Balanced Equity Mutual Fund    
Derivative Financial Instruments:    
Other Investments 0 0
Level 2 | Fixed Income Mutual Fund    
Derivative Financial Instruments:    
Other Investments 0 0
Level 3    
Derivative Financial Instruments:    
Total Assets 0 0
Derivative Financial Instruments:    
Total Liabilities 0 0
Total Net Assets/(Liabilities) 0 0
Level 3 | Money Market Funds    
Assets:    
Cash Equivalents – Money Market Mutual Funds 0 0
Level 3 | Over the Counter Swaps — Gas    
Derivative Financial Instruments:    
Derivative Asset 0 0
Derivative Financial Instruments:    
Derivative Liability 0 0
Level 3 | Over the Counter No Cost Collars – Gas    
Derivative Financial Instruments:    
Derivative Asset 0 0
Derivative Financial Instruments:    
Derivative Liability 0 0
Level 3 | Foreign Currency Contracts    
Derivative Financial Instruments:    
Derivative Asset 0 0
Derivative Financial Instruments:    
Derivative Liability 0 0
Level 3 | Balanced Equity Mutual Fund    
Derivative Financial Instruments:    
Other Investments 0 0
Level 3 | Fixed Income Mutual Fund    
Derivative Financial Instruments:    
Other Investments $ 0 $ 0
[1] Netting Adjustments represent the impact of legally-enforceable master netting arrangements that allow the Company to net gain and loss positions held with the same counterparties. The net asset or net liability for each counterparty is recorded as an asset or liability on the Company’s balance sheet.