Significant Accounting Policies - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Jan. 31, 2018 entity	Dec. 31, 2017 USD ($) country entity	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) country entity	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 1,261,223	$ 983,394	$ 1,277,439	$ 855,933	$ 1,175,893	$ 929,855	$ 1,231,910	$ 906,534	$ 4,377,989	$ 4,244,192	$ 4,291,659
Cash and cash equivalents		468,733				464,965				$ 468,733	464,965	458,673	$ 461,584
Receivables deemed uncollectible, period										2 years
Deferred online course development costs		60,949				54,713				$ 60,949	54,713
Deferred accreditation costs		3,179				3,035				3,179	3,035
Deferred costs, gross		176,402				160,554				176,402	160,554
Accumulated amortization of deferred costs		(112,274)				(102,806)				(112,274)	(102,806)
Unamortized balances of deferred financing costs		107,640				44,648				107,640	44,648
Advertising costs										277,960	274,870	278,296
Restricted cash included in operating cash inflows (outflows)										3,824	(7,686)	(932)
Restricted cash included in investing cash outflows										(39,848)	(28,063)	(15,452)
Cumulative effect of adoption to retained earnings		(946,236)				(1,037,701)				(946,236)	(1,037,701)
Accounting Standards Update 2015-17
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in current deferred tax assets						110,000					110,000
Decrease in current deferred tax liabilities						6,000					6,000
Accounting Standards Update 2014-09 | Pro Forma | Difference between Revenue Guidance in Effect before and after Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption to retained earnings		$ 2,000								2,000
Chile
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										$ 617,258	564,631	536,542
Variable Interest Entity, Primary Beneficiary
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of consolidated entities (entity) | entity										12
Number of countries with variable interest entities (country) | country		8								8
Revenues										$ 123,237	113,276	106,005
Cash and cash equivalents		$ 231,940				$ 169,074				231,940	169,074
Variable Interest Entity, Primary Beneficiary | Chile
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents		$ 101,000								$ 101,000
Number of entities with cash balances (entity) | entity		3								3
Variable Interest Entity, Primary Beneficiary | Subsequent Event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of VIE entities sold (entity) | entity	1
Variable Interest Entity, Primary Beneficiary | Central America & U.S. Campuses
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-operating investment income										$ 11,696	$ 11,061	$ 10,297