Segment Information (Summary of Inter-segment Eliminations) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues, net	$ 780,275	$ 654,015	$ 646,291	$ 734,375	$ 785,204	$ 718,597	$ 772,299	$ 784,221	$ 2,814,956	$ 3,060,321	$ 2,971,929
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues, net									(27,740)	(42,866)	(39,702)
Intersegment Eliminations [Member] | National Networks [Member]
Segment Reporting Information [Line Items]
Revenues, net									(22,617)	(32,762)	(33,600)
Intersegment Eliminations [Member] | International And Other [Member]
Segment Reporting Information [Line Items]
Revenues, net									$ (5,123)	$ (10,104)	$ (6,102)