Business Segments (Narrative) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($) TelevisionStation	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) TelevisionStation Segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment									6
Operating Revenues	$ 689,087	$ 674,766	$ 672,677	$ 659,436	$ 675,817	$ 657,225	$ 676,087	$ 582,717	$ 2,695,966	$ 2,591,846	$ 2,481,890
Television Broadcasting [Member]
Segment Reporting Information [Line Items]
Number of television broadcast stations owned | TelevisionStation	7								7
Education [Member]
Segment Reporting Information [Line Items]
Restructuring costs										9,065	11,852
Accrued restructuring costs	$ 4,600				8,500				$ 4,600	8,500
Non U.S. [Member]
Segment Reporting Information [Line Items]
Operating Revenues									657,000	637,000	624,000
Foreign assets	$ 124,000				$ 89,000				124,000	89,000
UNITED KINGDOM | Education [Member]
Segment Reporting Information [Line Items]
Operating Revenues									$ 345,000	320,000	312,000
Higher Education [Member] | Education [Member]
Segment Reporting Information [Line Items]
Restructuring costs										1,400	7,100
Test Preparation [Member] | Education [Member]
Segment Reporting Information [Line Items]
Restructuring costs										4,300
Kaplan International [Member] | Education [Member]
Segment Reporting Information [Line Items]
Restructuring costs										$ 2,900	$ 4,700