Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 21,969,756	$ 22,357,274
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 21,442,744	$ 21,755,202
Weighted Average Interest Rate	11.01%	10.66%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 527,012	$ 602,072
Weighted Average Interest Rate	7.24%	6.87%