Stockholders' Equity - Summary of Stock-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total stock-based compensation expense	$ 5,960	$ 7,180	$ 6,246
Instructional costs and services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total stock-based compensation expense	1,570	1,610	1,310
Selling and promotional
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total stock-based compensation expense	766	512	789
General and administrative
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total stock-based compensation expense	$ 3,624	$ 5,058	$ 4,147