Description Of Business And Basis Of Presentation (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) segment network	Mar. 31, 2017 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated earnings	$ 936,379			$ 766,725
Number of Operating Segments | segment	2
Number of Nationally Distributed Programming Networks | network	5
Program Rights Write Offs	$ 5,200	$ 400
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated earnings			$ 12,800