Pension Plans - Change in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
AOCI Attributable to Parent, Before Tax [Roll Forward]
Beginning balance	$ 3,214,398	$ 2,677,290
Ending balance	3,826,229	3,214,398
Pension Plan
AOCI Attributable to Parent, Before Tax [Roll Forward]
Beginning balance	15,230	9,573
Recognized during year - amortization of net actuarial losses	(697)	(398)
Occurring during year - effect of settlement	65	19
Occurring during year - net actuarial losses (gains)	(1,681)	5,369
Foreign exchange impact	703	667
Ending balance	$ 13,620	$ 15,230