Equity Awards - Stock-based compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 5,612	$ 4,646	$ 16,209	$ 12,714
Tax benefit	1,460	1,228	4,250	3,359
Stock-based compensation expense, net of tax	4,152	3,418	11,959	9,355
Instructional and support costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	1,802	1,365	5,190	3,871
General and administration
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	3,810	3,503	11,019	9,546
Restructuring costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 0	$ (222)	$ 0	$ (703)