Segment Information (Summary Of Inter-Segment Eliminations) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Revenues, net	$ 710,545	$ 684,832	$ 1,430,734	$ 1,391,411
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues, net	(5,222)	(6,081)	(6,977)	(7,186)
Intersegment Eliminations [Member] | National Networks [Member]
Segment Reporting Information [Line Items]
Revenues, net	(5,142)	(5,991)	(6,866)	(6,936)
Intersegment Eliminations [Member] | International And Other [Member]
Segment Reporting Information [Line Items]
Revenues, net	$ (80)	$ (90)	$ (111)	$ (250)