Significant Accounting Policies - New authoritative accounting guidance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Jan. 01, 2018
Excess tax benefit from share-based compensation, operating activities	$ 3.0
Forecast
Cumulative effective adjustment		$ 34.7

Amount of cash outflow for realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 20
-Section 55
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=65896087&loc=d3e11374-113907

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Balance Type:	credit
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