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Summary of Significant Accounting Policies - (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Oct. 01, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue recognition, new accounting pronouncement, timing	less than one year
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in restricted cash		$ (0.3)
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting for employee share-based payments			$ 0.0		$ (7.1)	$ 0.0	$ 0.0
Retained Earnings \| Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting for employee share-based payments				$ (7.1)