Reclassifications out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 2,370,410	$ 2,383,711	$ 2,605,379
Other comprehensive income (loss) before reclassification	(2,400)	56,000	59,400
Amounts reclassified from accumulated other comprehensive loss	(7,900)	(12,100)	(6,300)
Ending balance	2,696,184	2,370,410	2,383,711
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(882,671)	(926,577)	(979,675)
Ending balance	(893,027)	(882,671)	(926,577)
Pension Related Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(252,000)	(226,000)	(217,300)
Other comprehensive income (loss) before reclassification	(1,300)	(26,600)	(10,900)
Amounts reclassified from accumulated other comprehensive loss	1,900	600	2,200
Ending balance	(251,400)	(252,000)	(226,000)
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(646,500)	(739,700)	(799,300)
Other comprehensive income (loss) before reclassification	(5,900)	93,200	59,600
Amounts reclassified from accumulated other comprehensive loss	0	0	0
Ending balance	(652,400)	(646,500)	(739,700)
Loss on Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	15,800	39,100	36,900
Other comprehensive income (loss) before reclassification	4,800	(10,600)	10,700
Amounts reclassified from accumulated other comprehensive loss	(9,800)	(12,700)	(8,500)
Ending balance	$ 10,800	$ 15,800	$ 39,100