Goodwill and intangible assets - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 159.5	$ 159.5
Accumulated Amortization	16.8	14.0
Net Carrying Amount	142.7	145.5
Trademarks
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	40.1	40.1
Accumulated Amortization	4.0	3.4
Net Carrying Amount	36.1	36.7
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	84.4	84.4
Accumulated Amortization	8.8	7.3
Net Carrying Amount	75.6	77.1
Patents
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.5	34.5
Accumulated Amortization	3.8	3.2
Net Carrying Amount	30.7	31.3
Non-Compete
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0.5	0.5
Accumulated Amortization	0.2	0.1
Net Carrying Amount	$ 0.3	$ 0.4

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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