Summary of Significant Accounting Policies - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (55,060)	$ (625,733)
Other Comprehensive Gains and Losses Before Reclassifications	192,182	486,560
Amounts Reclassified From Other Comprehensive Loss	(152,598)	84,113
Ending balance	(15,476)	(55,060)
Gains and Losses on Derivative Financial Instruments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	4,623	(572,163)
Other Comprehensive Gains and Losses Before Reclassifications	205,697	493,936
Amounts Reclassified From Other Comprehensive Loss	(154,521)	82,850
Ending balance	55,799	4,623
Funded Status of the Pension and Other Post-Retirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(59,683)	(53,570)
Other Comprehensive Gains and Losses Before Reclassifications	(13,515)	(7,376)
Amounts Reclassified From Other Comprehensive Loss	1,923	1,263
Ending balance	$ (71,275)	$ (59,683)