Accumulated Other Comprehensive Income - Reclassifications out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2026	Mar. 31, 2025
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service credit	$ (156,635)		$ (283,517)		$ (341,725)	$ (559,667)
Other income (deductions), net	1,509		(1,727)		3,036	2,451
Income before income tax	(28,051)		(11,644)		56,367	(17,474)
Income taxes	6,217		2,728		(34,572)	5,086
Net (loss) income	(21,834)	$ 43,629	(8,916)	$ (3,472)	21,795	(12,388)
Gain (loss) on divestitures, net	(3,945)		(2,072)		109,264	(2,072)
Reclassification out of Accumulated Other Comprehensive Income | Net investment hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(586)		301		(465)	656
Post-retirement benefit plans | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income tax	217		226		506	454
Income taxes	(54)		(57)		(127)	(114)
Net (loss) income	163		169		379	340
Prior service credit | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service credit	58		89		115	180
Actuarial losses | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (deductions), net	159		137		391	274
Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income tax	(610)		553		(289)	1,376
Income taxes	154		(137)		73	(342)
Net (loss) income	(456)		416		(216)	1,034
Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income | Cash flow hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(24)		252		$ 176	720
Other | Reclassification out of Accumulated Other Comprehensive Income | Divestitures
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gain (loss) on divestitures, net	$ 0					(17,674)
Other | Reclassification out of Accumulated Other Comprehensive Income | Divestitures
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other current liabilities			$ 0			$ (6,844)