Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 20,614,487	$ 21,672,992	$ 21,359,026	$ 21,597,450
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 19,958,763	$ 20,944,581	$ 20,685,372	$ 20,860,973
Weighted Average Interest Rate	9.43%	8.26%	8.82%	8.23%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 655,724	$ 713,517	$ 673,654	$ 723,656
Weighted Average Interest Rate	5.03%	3.45%	4.18%	3.43%
Credit Cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance		$ 14,894		$ 12,821
Weighted Average Interest Rate		6.95%		4.97%