Summary of Significant Accounting Policies Basis of Consolidation Policy Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Ownership Interest to be Held for Consolidation [Line Items]
Unearned revenue	$ 77.0	$ 114.3
Maximum [Member]
Basis of Consolidation [Abstract]
Ownership Interest To Use Equity Method	50.00%
Ownership Interest To Use Cost Method	20.00%
Minimum [Member]
Basis of Consolidation [Abstract]
Ownership Interest to be Held for Consolidation	50.00%
Noncontrolling Interests [Abstract]
Ownership Interest to be Held for Consolidation	50.00%

Basis of Consolidation [Abstract]

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- Definition

Ownership Interest to be Held for Consolidation

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- Definition

Ownership Interest to be Held for Consolidation [Line Items]

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Entities in which the company has less than 20% investment and where they do not excercise significant influence are accounted for under the cost method.

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The equity method of accounting is used for entities in which the company has a 50% or less invesment and exercises significant influence.

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Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 13.A.3)
-URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 13.A.4(a).Q1)
-URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780

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