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Significant Accounting Policies - Schedule of impact of Topic 606 adoption on Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Deferred costs, net	$ 68,078		$ 64,128
Liabilities:
Deferred revenue and student deposits	351,951		312,422
Deferred income taxes	295,043		278,215
Equity:
Accumulated deficit	(548,617)		$ (946,236)
Balances Without Adoption of ASC 606
Assets
Deferred costs, net	62,319
Liabilities:
Deferred revenue and student deposits	352,449
Deferred income taxes	294,990
Equity:
Accumulated deficit	(554,821)
ASU 2014-09 \| Effect of Change Higher/(Lower)
Assets
Deferred costs, net	5,759
Liabilities:
Deferred revenue and student deposits	(498)
Deferred income taxes	53
Equity:
Accumulated deficit	$ 6,204	$ 1,400