Revenue Recognition - Graduation Fund (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Contract liability [Roll Forward]
Balance at beginning of period	$ 43,329	$ 37,400
Revenue deferred	21,358	18,791
Benefit redeemed	(17,947)	(15,792)
Balance at end of period	$ 46,740	$ 40,399