Goodwill and Intangible Assets - Goodwill (Details) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Changes in goodwill
December 31, 2016	$ 49,271
Acquired goodwill	46,217
Foreign currency translation adjustment	3,166
December 31, 2017	98,654
Content Business
Changes in goodwill
December 31, 2016	40,508
Acquired goodwill	46,217
Foreign currency translation adjustment	3,166
December 31, 2017	89,891
Other Category
Changes in goodwill
December 31, 2016	8,763
Acquired goodwill	0
Foreign currency translation adjustment	0
December 31, 2017	$ 8,763

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=64834752&loc=SL49117168-202975

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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