Business Segments (Information by Operating Segment) (Details 1) - USD ($) $ in Thousands	3 Months Ended					12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Document Fiscal Year Focus	2018
Operating Revenues	$ 659,436	$ 675,817	$ 657,225	$ 676,087	$ 582,717	$ 2,591,846	$ 2,481,890
Income (Loss) from Operations	44,214	49,459	26,950	49,741	10,253	136,403	222,869
Equity in earnings (losses) of affiliates, net	2,579	(4,697)	(532)	1,331	649	(3,249)	(7,937)
Interest Expense, Net	(6,699)	(4,919)	(7,758)	(7,862)	(6,766)	(27,305)	(32,297)
Non-operating pension and postretirement benefit income, net	21,386	17,657	17,621	18,620	18,801	72,699	80,665
Loss on marketable equity securities, net	(14,102)	0	0	0	0
Other income (expense), net	9,187	(2,640)	1,963	4,069	849	4,241	(12,642)
Income Before Income Taxes	56,565	54,860	38,244	65,899	23,786	182,789	250,658
Depreciation of property, plant and equipment	14,642	15,984	16,002	15,871	14,652	62,509	64,620
Amortization of Intangible Assets	10,384				6,836
Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets	10,384	12,975	11,235	19,755	6,836	50,801	28,274
Pension Expense	4,940	4,591	4,591	4,591	4,914	18,687	20,461
Identifiable Assets	3,083,495	3,216,141				3,216,141
Investments in Marketable Equity Securities	471,703	536,315				536,315
Investments in Affiliates	131,887	128,590				128,590
Prepaid Pension Cost	1,073,873	1,056,777				1,056,777
Total Assets	4,760,958	4,937,823				4,937,823
Operating Segments [Member] | Education [Member]
Segment Reporting Information [Line Items]
Operating Revenues	375,499	380,575	376,805	386,499	372,897	1,516,776	1,598,461
Income (Loss) from Operations	22,700	21,122	13,797	33,331	9,437	77,687	95,321
Depreciation of property, plant and equipment	7,606	7,912	8,085	8,325	8,584	32,906	41,187
Amortization of Intangible Assets	1,149	1,364	1,355	1,323	1,120	5,162	7,516
Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets	1,149	1,364	1,355	1,323	1,120	5,162	7,516
Pension Expense	2,664	2,431	2,430	2,153	2,706	9,720	11,803
Identifiable Assets	1,577,217	1,592,097				1,592,097
Operating Segments [Member] | Education [Member] | Kaplan Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenues	285	174	49	57	14	294	214
Income (Loss) from Operations	(8,895)	(8,124)	(7,631)	(6,045)	(8,063)	(29,863)	(29,279)
Depreciation of property, plant and equipment	154	175	130	135	130	570	555
Pension Expense	156	130	1,614	(889)	(336)	519	843
Identifiable Assets	26,070	21,624				21,624
Operating Segments [Member] | Education [Member] | Reportable Subsegments [Member] | Kaplan International [Member]
Segment Reporting Information [Line Items]
Operating Revenues	183,582	190,431	171,259	171,747	164,562	697,999	696,362
Income (Loss) from Operations	20,404	22,614	5,348	15,954	7,707	51,623	48,398
Depreciation of property, plant and equipment	3,974	3,821	3,780	3,609	3,682	14,892	17,523
Pension Expense	83	66	24	87	87	264	268
Identifiable Assets	1,147,327	1,115,919				1,115,919
Operating Segments [Member] | Education [Member] | Reportable Subsegments [Member] | Higher Education [Member]
Segment Reporting Information [Line Items]
Operating Revenues	99,830	103,264	105,210	111,840	111,111	431,425	501,784
Income (Loss) from Operations	1,355	(360)	1,493	13,140	2,446	16,719	39,196
Depreciation of property, plant and equipment	1,858	1,975	2,010	2,484	2,648	9,117	13,816
Pension Expense	1,406	1,318	467	1,742	1,742	5,269	6,544
Identifiable Assets	172,215	231,986				231,986
Operating Segments [Member] | Education [Member] | Reportable Subsegments [Member] | Test Preparation [Member]
Segment Reporting Information [Line Items]
Operating Revenues	59,151	60,320	72,680	75,730	64,568	273,298	286,556
Income (Loss) from Operations	521	1,300	7,330	5,741	(2,864)	11,507	9,599
Depreciation of property, plant and equipment	978	1,206	1,407	1,332	1,341	5,286	6,287
Pension Expense	729	689	244	911	911	2,755	3,072
Identifiable Assets	140,793	130,938				130,938
Operating Segments [Member] | Education [Member] | Reportable Subsegments [Member] | Professional (U.S.) [Member]
Segment Reporting Information [Line Items]
Operating Revenues	33,356	27,027	28,249	27,364	33,199	115,839	115,263
Income (Loss) from Operations	9,315	5,513	7,316	4,571	10,158	27,558	27,436
Depreciation of property, plant and equipment	642	735	758	765	783	3,041	3,006
Pension Expense	290	228	81	302	302	913	1,076
Identifiable Assets	90,812	91,630				91,630
Operating Segments [Member] | Education [Member] | Intersubsegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(705)	(641)	(642)	(239)	(557)	(2,079)	(1,718)
Income (Loss) from Operations	0	179	(59)	(30)	53	143	(29)
Operating Segments [Member] | Television Broadcasting [Member]
Segment Reporting Information [Line Items]
Operating Revenues	108,802	111,023	101,295	106,102	91,496	409,916	409,718
Income (Loss) from Operations	40,542	39,536	33,462	39,777	26,483	139,258	202,863
Depreciation of property, plant and equipment	3,071	3,476	3,118	2,991	2,594	12,179	9,942
Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets	1,408	3,406	1,071	970	902	6,349	251
Pension Expense	493	485	485	479	493	1,942	1,714
Identifiable Assets	451,070	455,884				455,884
Operating Segments [Member] | Healthcare [Member]
Segment Reporting Information [Line Items]
Operating Revenues	37,621	38,610	40,473	38,220	36,899	154,202	146,962
Income (Loss) from Operations	(1,391)	(2,947)	920	384	(926)	(2,569)	2,799
Depreciation of property, plant and equipment	653	1,154	1,166	1,194	1,069	4,583	2,805
Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets	1,808	2,187	2,420	1,644	1,654	7,905	6,701
Pension Expense	122	167	166	166	166	665	0
Identifiable Assets	125,041	129,856				129,856
Operating Segments [Member] | Other Businesses [Member]
Segment Reporting Information [Line Items]
Operating Revenues	137,538	145,660	138,652	145,266	81,425	511,003	326,888
Income (Loss) from Operations	(3,695)	6,698	(7,021)	(9,302)	(9,638)	(19,263)	(24,901)
Depreciation of property, plant and equipment	3,059	3,184	3,354	3,070	2,115	11,723	9,570
Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets	6,019	6,018	6,389	15,818	3,160	31,385	13,806
Pension Expense	289	282	277	249	317	1,125	1,118
Identifiable Assets	789,771	855,399				855,399
Corporate Office [Member]
Segment Reporting Information [Line Items]
Operating Revenues	0	0	0	0	0	0	0
Income (Loss) from Operations	(13,942)	(14,950)	(14,208)	(14,449)	(15,103)	(58,710)	(53,213)
Depreciation of property, plant and equipment	253	258	279	291	290	1,118	1,116
Amortization of Intangible Assets and Impairment of Goodwill and Other Long-Lived Assets	0	0	0	0	0	0	0
Pension Expense	1,372	1,226	1,233	1,544	1,232	5,235	5,826
Identifiable Assets	140,396	182,905				182,905
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating Revenues	$ (24)	$ (51)	$ 0	$ 0	$ 0	$ (51)	$ (139)