Summary of Quarterly Operating Results and Comprehensive Income (Loss) (Unaudited) (Quarterly Impact of Certain Items) (Details 2) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Impact of Certain Items [Line Items]
Reduction to operating expenses in association with spectrum repack agreement	$ 1,400	$ 800	$ 600	$ 200					$ 3,000
Earnings Per Share, Diluted, Reduction to operating expenses in association with spectrum repack agreement	$ 0.26	$ 0.14	$ 0.11	$ 0.04
Debt extinguishment costs, after tax			$ 8,600						8,600
Earnings per share, diluted, debt extinguishment costs			$ (1.60)
Gain on Lump Sum Pension Settlement and curtailment of postretirement benefit plans, after tax	$ 22,200								22,200
Earnings per share, diluted, settlement gain related to bulk lump sum pension offering and curtailment gain	$ 4.11
(Loss) Gain on Marketable Equity Securities, after tax	$ (33,600)	$ 33,600	$ (1,900)	$ (10,700)					(12,600)
Earnings per share, diluted, (loss) gain on marketable equity securities	$ (6.28)	$ 6.26	$ (0.36)	$ (1.94)
Non-operating gain from sales, write-ups and impairments of investments, and related to sales of land and businesses, including losses on guarantor obligations	$ (7,700)	$ 8,000	$ 1,800	$ 3,600					5,700
Earnings per share, Diluted, non-operating gain from sales, write-ups and impairments of investments, and related to sales of businesses, including loss on guarantor obligations	$ (1.43)	$ 1.48	$ 0.34	$ 0.65
Non-operating unrealized foreign currency gains (losses), after tax	$ (1,200)	$ (100)	$ (1,700)	$ 100	$ (2,100)	$ 900	$ 2,200	$ 1,100	(2,900)	$ 2,100
Earnings Per Share, Diluted, Foreign Currency Transaction Gain (Loss), Unrealized	$ (0.23)	$ (0.02)	$ (0.32)	$ 0.02	$ (0.37)	$ 0.16	$ 0.39	$ 0.19
Discrete Deferred Tax Benefit		$ 17,800							17,800
Earnings per share, Diluted, nonrecurring discrete deferred state tax benefit related to the release of valuation allowances		$ 3.31
Effective Income Tax Rate Reconciliation, Share-Based Compensation, Excess Tax Benefit				$ 1,800				$ 5,900	(1,731)	(6,023)	$ 0
Earnings Per Share, Diluted, Effective Income Tax Rate Reconciliation, Share-based Compensation Excess Tax Benefit				$ 0.33				$ 1.06
Net nonrecurring deferred tax benefit adjustment					$ 177,500					177,500
Earnings Per Share, Diluted, Net Deferred Tax Benefit					$ 31.68
Securities Subject to Mandatory Redemption [Member]
Quarterly Impact of Certain Items [Line Items]
Interest Expense, after tax			$ 6,200						6,200
Earnings per share, diluted, interest expense			$ (1.14)
Education [Member]
Quarterly Impact of Certain Items [Line Items]
Restructuring And Related Charges, Net of Tax					$ 4,500	$ 1,100	$ 400	$ 300		6,300
Earnings Per Share, Diluted, Restructuring And Related Charges					$ (0.81)	$ (0.20)	$ (0.06)	$ (0.05)
Graham Healthcare Group [Member]
Quarterly Impact of Certain Items [Line Items]
Impairment of Intangible Assets, After Tax		$ 5,800
Earnings per Share, Diluted, Impairment Of Intangible Assets		$ (1.08)
Other Businesses [Member]
Quarterly Impact of Certain Items [Line Items]
Goodwill and Other Long-Lived Asset Impairment, Net of Tax							$ 5,800			$ 5,800
Earnings Per Share, Diluted, Goodwill And Other Long-Lived Assets Impairment, Net of Tax							$ (1.03)
Kaplan University Transaction [Member] | Education [Member] | Higher Education [Member]
Quarterly Impact of Certain Items [Line Items]
Gain on Kaplan University transaction, after tax				$ 1,800					$ 1,800
Earnings per share, diluted, gain from Kaplan University transaction				$ 0.33