Lease and Other Commitments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leased Assets [Line Items]
Rent expense	$ 22.6	$ 23.7	$ 19.2
Rating Service Agreement with Nielsen
Operating Leased Assets [Line Items]
Remaining minimum amount committed	23.9
Other Broadcasting Services
Operating Leased Assets [Line Items]
Remaining minimum amount committed	3.0
Business Management Platform
Operating Leased Assets [Line Items]
Remaining minimum amount committed	$ 12.5