Derivatives - Summary of Derivative Assets and Liabilities (Details) - Cash Flow Hedging - Interest Rate Swap - USD ($) $ in Millions	Jun. 30, 2018	Sep. 30, 2017
Accumulated other comprehensive income
Derivatives, Fair Value [Line Items]
Other comprehensive income	$ 6.2	$ 0.0
Level 2 \| Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset	1.6	0.0
Level 2 \| Other non-current assets
Derivatives, Fair Value [Line Items]
Derivative asset	6.7	0.3
Level 2 \| Accrued expenses and other liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	0.4	1.1
Level 2 \| Other non-current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	$ 0.0	0.2
Maximum \| Accumulated other comprehensive income
Derivatives, Fair Value [Line Items]
Other comprehensive income		$ 0.1

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109247956&loc=SL51823488-111719

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant