Discontinued Operations Narrative (Details) - USD ($)			3 Months Ended		6 Months Ended			12 Months Ended
	Feb. 01, 2017	Jan. 31, 2017	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017		Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of Long-term Debt					$ 0	$ 589,661,000
Amended Secured Credit Facility | Term B Loans
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		$ 581,000,000				584,000,000
Proceeds from Divestiture of Business, Working Capital Adjustment			$ 3,000,000
Pretax (loss) gain on the disposal of discontinued operations			$ (952,000)	[1],[2]		34,510,000	[1],[2]	$ 33,000,000
Disposal Group, Including Discontinued Operation, Legal and Professional Fees						$ 10,000,000
Discontinued Operation, Amounts of Material Contingent Liabilities Remaining					$ 0

[1] (1) Results of operations for the Gracenote Companies are reflected through January 31, 2017, the date of the Gracenote Sale.

[2] (2)No depreciation expense or amortization expense was recorded by the Company in 2017 as the Gracenote Companies’ assets were held for sale as of December 31, 2016.