Significant Accounting Policies - Schedule of Impact of Topic 606 Adoption (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	Jan. 01, 2018
Statement of Operations data:
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
Direct costs									2,746,868	2,821,291	2,788,691
Income tax expense									(133,160)	91,308	(34,440)
Net income									370,930	93,764	$ 366,186
Assets
Deferred costs, net	66,835				60,931				66,835	60,931
Liabilities:
Deferred revenue and student deposits	193,226				184,116				193,226	184,116
Deferred income taxes	217,558				247,371				217,558	247,371
Equity:
Accumulated deficit	(530,919)				$ (946,236)				(530,919)	$ (946,236)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Statement of Operations data:
Revenues									3,350,224
Direct costs									2,752,486
Income tax expense									(132,821)
Net income									365,651
Assets
Deferred costs, net	59,799								59,799
Liabilities:
Deferred revenue and student deposits	193,226								193,226
Deferred income taxes	217,219								217,219
Equity:
Accumulated deficit	(537,616)								(537,616)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Statement of Operations data:
Revenues									0
Direct costs									(5,618)
Income tax expense									(339)
Net income									5,279
Assets
Deferred costs, net	7,036								7,036
Liabilities:
Deferred revenue and student deposits	0								0
Deferred income taxes	339								339
Equity:
Accumulated deficit	$ 6,697								$ 6,697			$ 1,400