Significant Accounting Policies - Equity Method Investments and Stock-Based Compensation (Details)	Dec. 31, 2017 item
Equity Method Investments
Number of countries in which the entity operates	23
Maximum
Equity Method Investments
General ownership percentage for equity method investments	50.00%
Minimum
Equity Method Investments
General ownership percentage for equity method investments	20.00%

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant