Goodwill and Intangible Assets - Goodwill (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2019 USD ($)
Goodwill
Balance at beginning of the period	$ 798,820
Acquisition activity	58,758
Translation and other	(5,957)
Balance at end of the period	851,621
GSG
Goodwill
Balance at beginning of the period	389,741
Acquisition activity	38,680
Translation and other	(581)
Balance at end of the period	427,840
CIG
Goodwill
Balance at beginning of the period	409,079
Acquisition activity	20,078
Translation and other	(5,376)
Balance at end of the period	$ 423,781