Other Non-Operating Income (Narrative) (Details) $ in Thousands	3 Months Ended									6 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) business
Schedule of Non-Operating Income [Line Items]
Impairment of a cost method investment	$ 4,800			$ 2,600							$ 7,327	$ 0	$ 2,697
Gain on acquiring a controlling interest in an equity affiliate											3,708	0	0
Net gain on cost method investments		$ 1,600	$ 2,600		$ 3,700	$ 1,300	$ 3,200	$ 8,500			4,209	5,080	11,663
Net gain (loss) on sale of businesses											213,302	(564)	8,157
Gain on sale of an equity affiliate											1,370	28,994	0
Loss on Guarantor Lease Obligations											1,014	1,075	17,518
Sale Of KHE Campuses Business [Member]
Schedule of Non-Operating Income [Line Items]
Loss on Guarantor Lease Obligations										$ 17,500	1,000	1,100	17,500
Gimlet Media [Member]
Schedule of Non-Operating Income [Line Items]
Gain on sale of an equity affiliate						$ 29,000
Framebridge [Member]
Schedule of Non-Operating Income [Line Items]
Gain on acquiring a controlling interest in an equity affiliate			$ 3,700
Megaphone [Member]
Schedule of Non-Operating Income [Line Items]
Net gain (loss) on sale of businesses	$ 209,800
Education [Member]
Schedule of Non-Operating Income [Line Items]
Net gain (loss) on sale of businesses													$ 8,200
Number Of Businesses Disposed | business													3
Education [Member] | Higher Education [Member] | Kaplan University Transaction [Member]
Schedule of Non-Operating Income [Line Items]
Net gain (loss) on sale of businesses									$ 4,300				$ 4,300
Gain Related to Contingent Consideration											$ 3,500	$ 1,400	$ 1,900