Revenue - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Remaining performance obligations recognition period	12 months
Accounts and notes receivable	$ 786,145	$ 535,176
Accounts receivable held for sale	15,434	34,744
Deferred revenue and student deposits, current	675,455	312,422
Revenue recognized	217,000
Capitalized contract cost	5,179	0
Capitalized contract cost, accumulated amortization	646	0
Amortization of capitalized costs	646
Disposal Group, Held-for-sale, Not Discontinued Operations
Disaggregation of Revenue [Line Items]
Deferred revenue and student deposits	$ 46,335	$ 94,951
Minimum
Disaggregation of Revenue [Line Items]
Contract cost, amortization period	2 years
Maximum
Disaggregation of Revenue [Line Items]
Contract cost, amortization period	4 years