Significant Accounting Policies - Troubled Debt Restructurings (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Percentage of Private Education Loans related to borrowers in school, grace or deferment	24.00%	24.00%
Interest rate offered to borrowers facing financial difficulty	4.00%
Interest rate offered to borrowers facing financial difficulty, period	2 years
Period of forbearance period to be classified as TDR	3 months
Period of forbearance	24 months
Period after grace period for forbearance allowance for loans	9 months
Forbearance period after grace period for loans	6 months
Percentage of loans granted forbearance (as a percentage)	47.00%	47.00%
Monthly payment that is smaller than the interest accrued on the loan in that month	$ 25