Summary of Significant Accounting Policies (Other Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Accounting Policies [Abstract]
Revenues	$ 741.1	$ 685.0
Net Income (Loss) Attributable to Parent	58.8	39.8
Net Income	$ 58.8	$ 39.8
Net Income Attributable to Common Shareholders per Common Share - Basic (usd per share)	$ 0.88	$ 0.60
Earnings Per Share, Diluted	$ 0.88	$ 0.59
Other Liabilities and Deferred Revenue, Noncurrent	$ 141.2		$ 138.1
Deferred Revenue, Additions	99.0
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized	(97.2)
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	$ 1.3