Equity Awards - Stock-based compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 5,632	$ 5,068
Tax benefit	1,479	1,334
Stock-based compensation expense, net of tax	4,153	3,734
Instructional and support costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	1,866	1,607
General and administration
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 3,766	$ 3,461