Discontinued Operations Narrative (Details) - USD ($)			3 Months Ended	12 Months Ended
	Feb. 01, 2017	Jan. 31, 2017	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt				$ 703,527,000	$ 27,842,000	$ 1,114,262,000
Gain (Loss) on Disposition of Business				(33,492,000)	0	0
Amended Secured Credit Facility | Term B Loans Facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt	$ 400,000,000
Discontinued Operations, Disposed of by Sale | Gracenote Companies
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Amounts of Material Contingent Liabilities Remaining				0
Disposal Group, Including Discontinued Operation, Consideration		$ 560,000,000
Proceeds from Divestiture of Businesses and Interests in Affiliates		$ 581,000,000
Transaction costs incurred to complete disposition				10,000,000	$ 3,000,000	$ 3,000,000
Proceeds from Divestiture of Business, Working Capital Adjustment			$ 3,000,000
Gain (Loss) on Disposition of Business				$ 33,000,000