Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 21,238,931	$ 21,701,229	$ 23,776,111
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 20,576,737	$ 20,968,061	$ 22,426,216
Weighted Average Interest Rate	9.14%	8.25%	8.42%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 662,194	$ 718,186	$ 757,953
Weighted Average Interest Rate	4.62%	3.43%	3.76%
Personal Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 0	$ 0	$ 582,552
Weighted Average Interest Rate	0.00%	0.00%	12.43%
Credit Cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 0	$ 14,982	$ 9,390
Weighted Average Interest Rate	0.00%	4.67%	(6.04%)