Goodwill and intangible assets (Schedule of Goodwill) (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Goodwill [Roll Forward]
Beginning Balance	$ 230.0	$ 229.7
Cumulative translation adjustment	(0.5)	0.3
Nu Finish acquisition	14.7
Ending Balance	244.2	230.0
Americas
Goodwill [Roll Forward]
Beginning Balance	213.8	213.7
Cumulative translation adjustment	(0.1)	0.1
Nu Finish acquisition	14.7
Ending Balance	228.4	213.8
International
Goodwill [Roll Forward]
Beginning Balance	16.2	16.0
Cumulative translation adjustment	(0.4)	0.2
Nu Finish acquisition	0.0
Ending Balance	$ 15.8	$ 16.2

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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