Significant Accounting Policies - Allowance for FFELP Loans and Loan Interest Income (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Percentage reimbursement on all qualifying default claims period two (as a percentage)	97.00%
Percentage reimbursement on all qualifying default claims period one (as a percentage)	98.00%
Variable rate	100.00%
Maximum loss exposure due to federal guarantee	3.00%
Basis points	0.0105
Loans in nonaccrual status	$ 0	$ 0