Equity Awards - Stock-based compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 3,025	$ 3,010
Tax benefit	777	759
Stock-based compensation expense, net of tax	2,248	2,251
Instructional and support costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	1,030	858
General and administration
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	1,995	1,673
Merger and integration costs
Schedule of stock-based compensation expense
Stock-based compensation expense included in operating expense	$ 0	$ 479