Goodwill and Intangible Assets - Goodwill (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2024 USD ($)
Goodwill
Balance at beginning of the period	$ 1,880,244
Acquisition activity	71,100
Translation adjustments	26,344
Balance at end of the period	1,977,688
GSG
Goodwill
Balance at beginning of the period	659,942
Acquisition activity	71,100
Translation adjustments	2,155
Balance at end of the period	733,197
CIG
Goodwill
Balance at beginning of the period	1,220,302
Acquisition activity	0
Translation adjustments	24,189
Balance at end of the period	$ 1,244,491