Pension Plans - Change in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
AOCI Attributable to Parent, Before Tax [Roll Forward]
Beginning balance	$ 2,296,034	$ 2,038,468
Ending balance	2,677,290	2,296,034
Pension Plan
AOCI Attributable to Parent, Before Tax [Roll Forward]
Beginning balance	5,408	30,213
Recognized during year - net actuarial losses	(241)	(1,421)
Occurring during year - settlement gain	0	82
Occurring during year - net actuarial losses	3,871	(21,253)
Plan amendments	91	0
Foreign exchange impact	444	(2,213)
Ending balance	$ 9,573	$ 5,408