Significant Accounting Policies - Schedule of impact of Topic 606 adoption on Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Deferred costs, net	$ 67,061		$ 64,128
Liabilities:
Deferred revenue and student deposits	675,455		312,422
Deferred income taxes	293,957		278,215
Equity:
Accumulated deficit	(772,283)		$ (946,236)
Balances Without Adoption of ASC 606
Assets
Deferred costs, net	62,528
Liabilities:
Deferred revenue and student deposits	682,088
Deferred income taxes	293,927
Equity:
Accumulated deficit	(783,419)
ASU 2014-09 | Effect of Change Higher/(Lower)
Assets
Deferred costs, net	4,533
Liabilities:
Deferred revenue and student deposits	(6,633)
Deferred income taxes	30
Equity:
Accumulated deficit	$ 11,136	$ 1,400