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Business Segments (Narrative) (Details) $ in Thousands		3 Months Ended								12 Months Ended
Business Segments (Narrative) (Details) $ in Thousands	Mar. 22, 2018 USD ($)	Dec. 31, 2020 USD ($) televisionStation automotiveDealership restaurant	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) segment automotiveDealership restaurant televisionStation	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Goodwill		$ 1,484,750				$ 1,388,279				$ 1,484,750	$ 1,388,279	$ 1,297,712
Number of reportable segments \| segment										6
Operating Revenues		787,011	$ 716,982	$ 652,871	$ 732,257	763,478	$ 738,820	$ 737,602	$ 692,199	$ 2,889,121	2,932,099	2,695,966
Clyde's Restaurant Group [Member]
Segment Reporting Information [Line Items]
Accelerated Depreciation										5,700
Television Broadcasting [Member]
Segment Reporting Information [Line Items]
Goodwill		$ 190,815				190,815				$ 190,815	190,815	190,815
Number of television broadcast stations owned \| televisionStation		7								7
Other Businesses [Member]
Segment Reporting Information [Line Items]
Goodwill		$ 115,909				61,859				$ 115,909	61,859	15,860
Number of dealerships \| automotiveDealership		3								3
Number of Restaurants \| restaurant		11								11
Education [Member]
Segment Reporting Information [Line Items]
Goodwill		$ 852,228				809,807				$ 852,228	809,807	797,548
Accrued restructuring costs		4,700				1,300				4,700	1,300
Non U.S. [Member]
Segment Reporting Information [Line Items]
Operating Revenues										642,000	691,000	657,000
Foreign assets		442,000				431,000				442,000	431,000
UNITED KINGDOM \| Education [Member]
Segment Reporting Information [Line Items]
Operating Revenues										375,000	384,000	345,000
Higher Education [Member] \| Education [Member]
Segment Reporting Information [Line Items]
Goodwill		63,240				63,240				63,240	63,240	63,240
Test Preparation [Member] \| Education [Member]
Segment Reporting Information [Line Items]
Goodwill			64,700
Kaplan International [Member] \| Education [Member]
Segment Reporting Information [Line Items]
Goodwill		634,749				$ 595,604				634,749	$ 595,604	$ 583,424
Professional (U.S.) [Member] \| Education [Member]
Segment Reporting Information [Line Items]
Goodwill			$ 89,500
Kaplan University Transaction [Member] \| Higher Education [Member] \| Education [Member] \| Purdue University Global [Member]
Segment Reporting Information [Line Items]
Accounts receivable		87,300								87,300
Accounts receivable, noncurrent		$ 19,900								$ 19,900
Advance Related To Kaplan University Transaction	$ 20,000