Loans Held for Investment - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Jul. 01, 2006	Jun. 30, 2006	Sep. 30, 1993
Receivables [Abstract]
Percent of private loans indexed to LIBOR	51.00%		52.00%
Tier 1 of government guarantee (at least)	97.00%			97.00%
Tier 2 of government guarantee					98.00%
Tier 3 of government guarantee						100.00%
Gain from sale	$ 9,881	$ 399,111
Proceeds from sale of loans	95,000	3,160,000
Net proceeds from sales of loans held for investment, principal	89,000	2,970,000
Net proceeds from sales of loans held for investment, capitalized interest	$ 6,000	$ 193,000
Estimated weighted average life of student loans	4 years 9 months 18 days		4 years 8 months 12 days