Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 22,575,432	$ 21,730,621
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 21,858,270	$ 20,984,491
Weighted Average Interest Rate	8.38%	8.22%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 690,540	$ 734,289
Weighted Average Interest Rate	3.51%	3.41%
Credit Cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 26,622	$ 11,841
Weighted Average Interest Rate	3.95%	0.78%