Equity Awards - Tax windfall (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Schedule of information regarding share-based payment arrangements
Tax windfall related to share-based payment arrangements	$ 3.5	$ 0.6

Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=SL79508275-113901

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