Segment Information (Summary Of Inter-Segment Eliminations) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues, net	$ 648,023	$ 634,646	$ 2,078,757	$ 2,026,057
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues, net	(6,179)	(5,087)	(13,156)	(12,273)
Intersegment Eliminations [Member] | National Networks [Member]
Segment Reporting Information [Line Items]
Revenues, net	(6,179)	(5,079)	(13,045)	(12,015)
Intersegment Eliminations [Member] | International And Other [Member]
Segment Reporting Information [Line Items]
Revenues, net	$ 0	$ (8)	$ (111)	$ (258)