Segment Reporting (Schedule of Geographic Information) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 782,800,000	$ 726,800,000	$ 714,200,000	$ 683,500,000	$ 759.2	$ 708.6	$ 710.5	$ 669.7	$ 2,907,300,000	$ 2,848,000,000.0	$ 2,743,700,000
Long-lived assets	296,800,000				328,300,000				296,800,000	328,300,000	355,400,000
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									2,056,800,000	1,956,400,000	1,887,600,000
Long-lived assets	212,500,000				239,500,000				212,500,000	239,500,000	243,900,000
Foreign [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									850,500,000	891,600,000	856,100,000
Long-lived assets	$ 84,300,000				$ 88,800,000				$ 84,300,000	$ 88,800,000	$ 111,500,000