Legal and Regulatory Matters - Turkish Regulation and Internal Investigation (Details) - USD ($) $ 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
Loss Contingencies [Line Items]
Assets	$ 6,769,636				$ 7,391,285				$ 6,769,636	$ 7,391,285
Liabilities	4,704,294				5,390,006				4,704,294	5,390,006
Revenues	913,710	$ 787,102	$ 1,017,196	$ 632,216	951,189	$ 818,601	$ 1,017,108	$ 598,978	3,350,224	3,385,876	$ 3,301,864
Operating income (loss)	139,807	$ 25,576	$ 218,218	$ (92,619)	140,116	$ 24,860	$ 196,047	$ (119,030)	290,982	241,993	290,677
Kendall College, St. Augustine, Walden University, and NewSchool of Architecture and Design
Loss Contingencies [Line Items]
Letters of credit outstanding, amount	139,000				136,900				139,000	136,900
Variable Interest Entity, Primary Beneficiary
Loss Contingencies [Line Items]
Assets	1,196,813				1,419,579				1,196,813	1,419,579
Liabilities	$ 274,744				$ 449,561				274,744	449,561
Revenues									$ 100,227	$ 123,237	$ 113,276