Goodwill and Intangible Assets - Goodwill (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2019 USD ($)
Goodwill
Balance at beginning of the period	$ 798,820
Acquisition activity	38,680
Translation and other	(9,824)
Balance at end of the period	827,676
GSG
Goodwill
Balance at beginning of the period	389,741
Acquisition activity	38,680
Translation and other	(1,751)
Balance at end of the period	426,670
CIG
Goodwill
Balance at beginning of the period	409,079
Acquisition activity	0
Translation and other	(8,073)
Balance at end of the period	$ 401,006