Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 20,982,244	$ 21,290,038	$ 21,476,000	$ 21,820,708
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 20,480,805	$ 20,704,907	$ 20,961,775	$ 21,227,153
Weighted Average Interest Rate	10.91%	10.79%	10.96%	10.72%
FFELP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Balance	$ 501,439	$ 585,131	$ 514,225	$ 593,555
Weighted Average Interest Rate	7.73%	7.10%	7.48%	6.98%