Segment and Geographic Information (Revenue By Geographic Segment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Revenue	$ 1,255,631	$ 1,241,824	$ 1,164,039
United States [Member]
Revenue	514,400	487,300	475,500
Germany [Member]
Revenue	185,400	193,300	164,700
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue	1,311,494	1,241,824	1,164,039
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | United States [Member]
Revenue	541,700
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Germany [Member]
Revenue	197,200
Operating Segments [Member]
Revenue	1,255,631	1,241,824	1,164,039
Operating Segments [Member] | Americas [Member]
Revenue	537,548	511,237	500,879
Operating Segments [Member] | Europe [Member]
Revenue	464,666	485,851	435,183
Operating Segments [Member] | Asia Pacific [Member]
Revenue	253,417	$ 244,736	$ 227,977
Operating Segments [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue	1,311,494
Operating Segments [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Americas [Member]
Revenue	565,362
Operating Segments [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Europe [Member]
Revenue	494,864
Operating Segments [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Asia Pacific [Member]
Revenue	$ 251,268