Revenue Recognition - Graduation Fund (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Graduation Fund [Roll Forward]
Balance at beginning of period	$ 52,024	$ 53,314
Revenue deferred	4,368	6,516
Benefit redeemed	(5,182)	(5,421)
Balance at end of period	$ 51,210	$ 54,409