Equity Awards - Stock-based compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 4,168	$ 3,859	$ 8,068	$ 6,884
Tax benefit	1,131	993	2,131	1,770
Stock-based compensation expense, net of tax	3,037	2,866	5,937	5,114
Instructional and support costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	1,281	1,356	2,506	2,386
General and administration
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	3,368	2,503	6,043	4,498
Restructuring costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ (481)	$ 0	$ (481)	$ 0