Significant Accounting Policies - Deferred Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Deferred revenue and student deposits	$ 21,776	$ 22,104
Scholarship assistance	$ 54,600	$ 45,600	$ 26,100