Goodwill and Other Intangible Assets (Other Intangible Assets) (Details 2) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Amortized Intangible Assets [Line Items]
Gross Carrying Amount		$ 425,320	$ 362,073
Accumulated Amortization		165,265	124,097
Net Carrying Amount		260,055	237,976
Indefinite-Lived Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets		114,752	102,195
Trade Names and Trademarks [Member]
Indefinite-Lived Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets		95,802	82,745
FCC licenses [Member]
Indefinite-Lived Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets		18,800	18,800
Licensure and Accreditation [Member]
Indefinite-Lived Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets		150	650
Student and Customer Relationships [Member]
Amortized Intangible Assets [Line Items]
Gross Carrying Amount		281,639	260,464
Accumulated Amortization		106,235	83,690
Net Carrying Amount		$ 175,404	$ 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		$ 71,870	$ 50,286
Accumulated Amortization		37,858	25,596
Net Carrying Amount		$ 34,012	$ 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		2,972	1,668
Net Carrying Amount		14,428	15,732
Databases and Technology [Member]
Amortized Intangible Assets [Line Items]
Gross Carrying Amount		28,788	19,563
Accumulated Amortization		8,537	5,008
Net Carrying Amount		$ 20,251	$ 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		$ 1,093	$ 930
Accumulated Amortization		778	467
Net Carrying Amount		$ 315	$ 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		$ 24,530	$ 13,430
Accumulated Amortization		8,885	7,668
Net Carrying Amount		$ 15,645	$ 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.