Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 22,357,274	$ 22,575,432
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 21,755,202	$ 21,858,270
Weighted Average Interest Rate	10.66%	8.38%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 602,072	$ 690,540
Weighted Average Interest Rate	6.87%	3.51%
Credit Cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 0	$ 26,622
Weighted Average Interest Rate	0.00%	3.95%