Derivatives - Summary of Gains and Losses (Net of Reclassifications Into Income) (Details) - Interest Rate Swap - Designated as Hedging Instrument - Cash Flow Hedging - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest expense
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) on derivative instruments	$ 0.3	$ 1.2	$ 1.0	$ 1.5
Other comprehensive income (loss)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) on derivative instruments	$ 2.1	$ (0.7)	$ 6.2	$ (0.4)

Amount after tax and reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580

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