Segment Information (Summary Of Inter-Segment Eliminations) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues, net	$ 729,597	$ 634,646	$ 684,832	$ 706,579	$ 678,950	$ 632,165	$ 601,138	$ 668,682	$ 2,755,654	$ 2,580,935	$ 2,175,641
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues, net									(15,382)	(7,010)	(2,502)
Intersegment Eliminations [Member] | National Networks [Member]
Segment Reporting Information [Line Items]
Revenues, net									(14,963)	(6,719)	(1,802)
Intersegment Eliminations [Member] | International And Other [Member]
Segment Reporting Information [Line Items]
Revenues, net									$ (419)	$ (291)	$ (700)