Business Segments (Information by Operating Segment) (Details 2) - 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]
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
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									187,357	206,941	301,684
Amortization of intangible assets and impairment of goodwill and other long-lived assets									86,950	62,395	55,523
Income (loss) from operations	46,201	40,244	5,877	8,085	30,312	16,268	57,963	40,003	100,407	144,546	246,161
Equity in earnings (losses) of affiliates, net	2,937	4,092	1,182	(1,547)	3,835	4,683	1,467	1,679	6,664	11,664	14,473
Interest expense, net									(34,439)	(23,628)	(32,549)
Debt extinguishment costs									0	0	(11,378)
Non-operating pension and postretirement benefit income, net	18,287	10,489	12,136	18,403	111,061	19,556	12,253	19,928	59,315	162,798	120,541
Gain (loss) on marketable equity securities, net	61,926	59,364	39,890	(100,393)	49,407	17,404	7,791	24,066	60,787	98,668	(15,843)
Other income, net	203,524	222	8,100	2,688	(3,704)	5,556	1,228	29,351	214,534	32,431	2,103
Income Before Income Taxes	317,743	108,054	60,762	(79,291)	185,117	58,165	73,895	109,302	407,268	426,479	323,508
Depreciation of property, plant and equipment	16,159	18,481	22,913	16,704	16,495	15,351	13,884	13,523	74,257	59,253	56,722
Pension service cost									22,656	20,422	18,221
Capital Expenditures									65,874	93,947	98,067
Identifiable Assets	4,006,935				3,891,557				4,006,935	3,891,557
Marketable equity securities	573,102				585,080				573,102	585,080
Investments in Affiliates	155,777				162,249				155,777	162,249
Prepaid Pension Cost	1,708,305				1,292,350				1,708,305	1,292,350
Total Assets	6,444,119				5,931,236				6,444,119	5,931,236
Amortization of Intangible Assets	14,138	14,150	14,327	14,165	13,731	13,572	12,880	13,060	56,780	53,243	47,414
Impairment of Long-Lived Assets	342	$ 1,916	$ 11,511	$ 16,401	8,087	$ 372	$ 693	$ 0	30,170	9,152	8,109
Operating Segments [Member] | Education [Member]
Segment Reporting Information [Line Items]
Operating Revenues									1,305,713	1,451,750	1,451,015
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									41,056	63,680	106,498
Amortization of intangible assets and impairment of goodwill and other long-lived assets									29,452	15,608	9,362
Income (loss) from operations									11,604	48,072	97,136
Depreciation of property, plant and equipment									31,759	25,655	28,099
Pension service cost									10,024	10,385	8,753
Capital Expenditures									33,553	57,246	54,159
Identifiable Assets	1,975,104				2,032,425				1,975,104	2,032,425
Amortization of Intangible Assets									17,174	14,915	9,362
Impairment of Long-Lived Assets									12,278	693	0
Operating Segments [Member] | Education [Member] | Reportable Subsegments [Member] | Kaplan International [Member]
Segment Reporting Information [Line Items]
Operating Revenues									653,892	750,245	719,982
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									15,248	42,129	70,315
Income (loss) from operations									15,248	42,129	70,315
Depreciation of property, plant and equipment									19,562	15,394	15,755
Pension service cost									433	454	298
Capital Expenditures									24,085	48,362	44,469
Identifiable Assets	1,455,722				1,455,122				1,455,722	1,455,122
Operating Segments [Member] | Education [Member] | Reportable Subsegments [Member] | Higher Education [Member]
Segment Reporting Information [Line Items]
Operating Revenues									316,095	305,672	342,085
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									24,364	13,960	15,217
Income (loss) from operations									24,364	13,960	15,217
Depreciation of property, plant and equipment									3,082	2,883	4,826
Pension service cost									4,150	4,535	4,310
Capital Expenditures									3,234	3,463	4,045
Identifiable Assets	187,123				196,761				187,123	196,761
Operating Segments [Member] | Education [Member] | Reportable Subsegments [Member] | Supplemental Education [Member]
Segment Reporting Information [Line Items]
Operating Revenues									327,087	388,814	390,289
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									19,705	34,487	47,704
Income (loss) from operations									19,705	34,487	47,704
Depreciation of property, plant and equipment									8,724	7,132	7,037
Pension service cost									4,207	4,734	3,773
Capital Expenditures									6,030	5,362	5,526
Identifiable Assets	274,687				312,454				274,687	312,454
Operating Segments [Member] | Education [Member] | Kaplan Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenues									12,643	9,480	1,142
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									(18,266)	(26,891)	(26,702)
Income (loss) from operations									(47,718)	(42,499)	(36,064)
Depreciation of property, plant and equipment									391	246	481
Pension service cost									1,234	662	372
Capital Expenditures									204	59	119
Identifiable Assets	57,572				68,088				57,572	68,088
Operating Segments [Member] | Education [Member] | Intersubsegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(4,004)	(2,461)	(2,483)
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									5	(5)	(36)
Income (loss) from operations									5	(5)	(36)
Operating Segments [Member] | Television Broadcasting [Member]
Segment Reporting Information [Line Items]
Operating Revenues									525,212	463,464	505,549
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									199,938	166,076	216,165
Amortization of intangible assets and impairment of goodwill and other long-lived assets									5,440	13,408	5,632
Income (loss) from operations									194,498	152,668	210,533
Depreciation of property, plant and equipment									13,830	12,817	13,204
Pension service cost									3,263	3,025	2,188
Capital Expenditures									13,470	19,362	27,013
Identifiable Assets	453,988				463,689				453,988	463,689
Operating Segments [Member] | Manufacturing [Member]
Segment Reporting Information [Line Items]
Operating Revenues									416,137	449,053	487,619
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									40,427	46,809	53,597
Amortization of intangible assets and impairment of goodwill and other long-lived assets									28,099	26,342	24,746
Income (loss) from operations									12,328	20,467	28,851
Depreciation of property, plant and equipment									10,333	10,036	9,515
Pension service cost									1,424	80	72
Capital Expenditures									8,034	11,218	14,806
Identifiable Assets	551,611				564,251				551,611	564,251
Operating Segments [Member] | Graham Healthcare Group [Member]
Segment Reporting Information [Line Items]
Operating Revenues									198,196	161,768	149,275
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									30,327	14,319	6,454
Amortization of intangible assets and impairment of goodwill and other long-lived assets									4,220	6,411	14,855
Income (loss) from operations									26,107	7,908	(8,401)
Depreciation of property, plant and equipment									1,665	2,314	2,577
Pension service cost									543	492	573
Capital Expenditures									2,481	2,303	1,741
Identifiable Assets	160,654				160,033				160,654	160,033
Operating Segments [Member] | Other Businesses [Member]
Segment Reporting Information [Line Items]
Operating Revenues									445,491	406,731	102,608
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									(72,413)	(32,786)	(28,169)
Amortization of intangible assets and impairment of goodwill and other long-lived assets									19,739	626	928
Income (loss) from operations									(92,152)	(33,412)	(29,097)
Depreciation of property, plant and equipment									15,964	7,556	2,320
Pension service cost									1,698	1,640	1,301
Capital Expenditures									8,256	3,703	348
Identifiable Assets	517,533				567,395				517,533	567,395
Corporate office [Member]
Segment Reporting Information [Line Items]
Operating Revenues									0	0	0
Operating Income before Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets.									(51,978)	(51,157)	(52,861)
Amortization of intangible assets and impairment of goodwill and other long-lived assets									0	0	0
Income (loss) from operations									(51,978)	(51,157)	(52,861)
Depreciation of property, plant and equipment									706	875	1,007
Pension service cost									5,704	4,800	5,334
Capital Expenditures									80	115	0
Identifiable Assets	$ 348,045				$ 103,764				348,045	103,764
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating Revenues									$ (1,628)	$ (667)	$ (100)