Equity Awards - Stock-based compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 3,875	$ 2,499	$ 10,759	$ 9,075
Tax benefit	997	651	2,767	2,333
Stock-based compensation expense, net of tax	2,878	1,848	7,992	6,742
Instructional and support costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	1,390	945	3,776	2,820
General and administration
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	2,485	2,077	6,983	5,888
Merger and integration costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 0	$ (523)	$ 0	$ 367