Discontinued Operations Narrative (Details) - USD ($)			3 Months Ended	12 Months Ended
	Feb. 01, 2017	Jan. 31, 2017	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Business				$ 0	$ (33,492,000)	$ 0
Repayments of long-term debt				0	703,527,000	27,842,000
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]
Disposal Group, Including Discontinued Operation, Consideration		$ 560,000,000
Proceeds from Divestiture of Businesses and Interests in Affiliates		$ 581,000,000
Proceeds from Divestiture of Business, Working Capital Adjustment			$ 3,000,000
Gain (Loss) on Disposition of Business					33,000,000
Transaction costs incurred to complete disposition					$ 10,000,000	$ 3,000,000
Discontinued Operation, Amounts of Material Contingent Liabilities Remaining				$ 0