Acquisitions and Divestitures - ACG unaudited pro-forma information (Details) - ACG Materials - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Revenues	$ 1,604.1	$ 1,594.4
Income before income taxes	$ 97.6	$ 133.6

The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

Name:	us-gaap_BusinessAcquisitionsProFormaRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration