Goodwill and Intangible Assets - Intangibles Impairment (Details) - USD ($) $ in Thousands	2 Months Ended	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Amortization expenses		$ 10,278			$ 10,278
Impairment of intangible assets		2,000
Trade names
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Indefinite-lived intangible assets	$ 185,700	185,700			185,700		$ 7,300
Impairment of intangible assets		2,000	$ 3,400	$ 0		$ 0
Student relationships
Finite Lived And Indefinite Lived Intangible Assets By Major Class [Line Items]
Useful life - acquired	3 years
Finite-lived intangible assets	$ 156,777	156,777			156,777		$ 0
Amortization expenses		$ 9,200			$ 9,200