Segment Information (Summary Of Inter-Segment Eliminations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Revenues, net	$ 740,823	$ 720,189
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues, net	(3,595)	(1,755)
Intersegment Eliminations [Member] | National Networks [Member]
Segment Reporting Information [Line Items]
Revenues, net	(2,535)	(1,724)
Intersegment Eliminations [Member] | International And Other [Member]
Segment Reporting Information [Line Items]
Revenues, net	$ (1,060)	$ (31)