Summary of Significant Accounting Policies (Other Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020
Accounting Policies [Abstract]
Revenues	$ 717,700,000	$ 767,500,000	$ 2,220,800,000	$ 2,175,700,000
Net Income (Loss) Attributable to Parent	49,200,000	93,900,000	195,100,000	$ 180,600,000
Net Income	$ 49,200,000	$ 93,900,000	$ 195,100,000
Net Income Attributable to Common Shareholders per Common Share - Basic (usd per share)	$ 0.74	$ 1.41	$ 2.94	$ 2.71
Earnings Per Share, Diluted	$ 0.74	$ 1.40	$ 2.92	$ 2.68
Other Liabilities and Deferred Revenue, Noncurrent	$ 136,200,000		$ 136,200,000		$ 138,100,000
Deferred Revenue, Additions	378,200,000
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized	(380,900,000)
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	$ 800,000		$ 800,000