Discontinued operations and dispositions - (Loss) income before income taxes attributable to the Environmental Sciences business (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($)
Environmental Sciences Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income before income taxes	$ 2.2

Amount of operating income (loss) attributable to disposal group, including, but not limited to, discontinued operation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721673-107760

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration