Stockholders' Equity - Summary of Stock-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total stock-based compensation expense	$ 7,654	$ 7,075	$ 5,960
Instructional costs and services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total stock-based compensation expense	1,480	1,535	1,570
Selling and promotional
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total stock-based compensation expense	771	1,007	766
General and administrative
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total stock-based compensation expense	$ 5,403	$ 4,533	$ 3,624