Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 21,290,038	$ 20,963,257	$ 21,820,708	$ 21,764,891
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 20,704,907	$ 20,259,956	$ 21,227,153	$ 21,054,698
Weighted Average Interest Rate	10.79%	8.69%	10.72%	8.53%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 585,131	$ 675,081	$ 593,555	$ 682,768
Weighted Average Interest Rate	7.10%	4.01%	6.98%	3.76%
Credit Cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 0	$ 28,220	$ 0	$ 27,425
Weighted Average Interest Rate	0.00%	4.00%	0.00%	3.97%