Equity Awards - Stock-based compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 5,844	$ 2,914	$ 11,781	$ 8,569
Tax benefit	1,607	1,151	3,253	3,384
Stock-based compensation expense, net of income tax	4,237	1,763	8,528	5,185
Instruction and educational support
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	695	548	1,813	1,363
Marketing
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	278		278
Admissions advisory
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	8		8
General and administration
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	2,591	$ 2,366	7,410	$ 7,206
Merger costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 2,272		$ 2,272