Pension Plans - Change in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
AOCI Attributable to Parent, Before Tax [Roll Forward]
Beginning balance	$ 2,677,290	$ 2,296,034
Ending balance	3,214,398	2,677,290
Pension Plan
AOCI Attributable to Parent, Before Tax [Roll Forward]
Beginning balance	9,573	5,408
Recognized during year - net actuarial losses	(398)	(241)
Occurring during year - settlement gain	19	0
Occurring during year - net actuarial losses (gains)	5,369	3,871
Plan amendments	0	91
Foreign exchange impact	667	444
Ending balance	$ 15,230	$ 9,573