Goodwill and Other Intangible Assets (Other Intangible Assets) (Details 2) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Amortized Intangible Assets [Line Items]
Gross Carrying Amount		$ 365,803	$ 362,073
Accumulated Amortization		135,129	124,097
Net Carrying Amount		230,674	237,976
Indefinite-Lived Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets, Net		103,916	102,195
Trade Names and Trademarks [Member]
Indefinite-Lived Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets, Net		84,966	82,745
FCC licenses [Member]
Indefinite-Lived Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets, Net		18,800	18,800
Licensure and Accreditation [Member]
Indefinite-Lived Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets, Net		150	650
Student and Customer Relationships [Member]
Amortized Intangible Assets [Line Items]
Gross Carrying Amount		261,022	260,464
Accumulated Amortization		91,658	83,690
Net Carrying Amount		$ 169,364	$ 176,774
Student and Customer Relationships [Member] | Minimum [Member]
Amortized Intangible Assets [Line Items]
Useful Life	[1]	2 years	1 year
Student and Customer Relationships [Member] | Maximum [Member]
Amortized Intangible Assets [Line Items]
Useful Life	[1]	10 years	10 years
Trade Names and Trademarks [Member]
Amortized Intangible Assets [Line Items]
Gross Carrying Amount		$ 50,858	$ 50,286
Accumulated Amortization		26,917	25,596
Net Carrying Amount		$ 23,941	$ 24,690
Trade Names and Trademarks [Member] | Minimum [Member]
Amortized Intangible Assets [Line Items]
Useful Life		2 years	2 years
Trade Names and Trademarks [Member] | Maximum [Member]
Amortized Intangible Assets [Line Items]
Useful Life		10 years	10 years
Network Affiliation Agreements [Member]
Amortized Intangible Assets [Line Items]
Useful Life		10 years	10 years
Gross Carrying Amount		$ 17,400	$ 17,400
Accumulated Amortization		2,103	1,668
Net Carrying Amount		15,297	15,732
Databases and Technology [Member]
Amortized Intangible Assets [Line Items]
Gross Carrying Amount		21,988	19,563
Accumulated Amortization		5,929	5,008
Net Carrying Amount		$ 16,059	$ 14,555
Databases and Technology [Member] | Minimum [Member]
Amortized Intangible Assets [Line Items]
Useful Life		3 years	3 years
Databases and Technology [Member] | Maximum [Member]
Amortized Intangible Assets [Line Items]
Useful Life		6 years	6 years
Non-compete Agreements [Member]
Amortized Intangible Assets [Line Items]
Gross Carrying Amount		$ 1,105	$ 930
Accumulated Amortization		580	467
Net Carrying Amount		$ 525	$ 463
Non-compete Agreements [Member] | Minimum [Member]
Amortized Intangible Assets [Line Items]
Useful Life		2 years	2 years
Non-compete Agreements [Member] | Maximum [Member]
Amortized Intangible Assets [Line Items]
Useful Life		5 years	5 years
Other [Member]
Amortized Intangible Assets [Line Items]
Gross Carrying Amount		$ 13,430	$ 13,430
Accumulated Amortization		7,942	7,668
Net Carrying Amount		$ 5,488	$ 5,762
Other [Member] | Minimum [Member]
Amortized Intangible Assets [Line Items]
Useful Life		1 year	1 year
Other [Member] | Maximum [Member]
Amortized Intangible Assets [Line Items]
Useful Life		8 years	8 years

[1] As of December 31, 2017, the student and customer relationships’ minimum useful life was 1 year.