Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 20,963,257	$ 21,389,370	$ 21,764,891	$ 21,559,053
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 20,259,956	$ 20,654,285	$ 21,054,698	$ 20,818,476
Weighted Average Interest Rate	8.69%	8.22%	8.53%	8.22%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 675,081	$ 723,391	$ 682,768	$ 728,810
Weighted Average Interest Rate	4.01%	3.41%	3.76%	3.41%
Credit Cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 28,220	$ 11,694	$ 27,425	$ 11,767
Weighted Average Interest Rate	4.00%	6.64%	3.97%	3.71%