Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 22,916,916	$ 21,969,756
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 22,916,916	$ 21,442,744
Weighted Average Interest Rate	10.59%	11.01%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 0	$ 527,012
Weighted Average Interest Rate	0.00%	7.24%