Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 21,534,883	$ 21,613,919	$ 21,238,931
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 21,121,545	$ 21,039,701	$ 20,576,737
Weighted Average Interest Rate	10.81%	10.86%	9.14%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 413,338	$ 574,218	$ 662,194
Weighted Average Interest Rate	7.45%	7.19%	4.62%