Allowance for Credit Losses - Amortized Cost Basis of Financing Receivables with Loan Modifcations (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2022
Interest Rate Reduction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 17,621	$ 23,117
% of Total Class of Financing Receivable	0.09%	0.12%
Combination - Interest Rate Reduction and Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 96,015	$ 162,049
% of Total Class of Financing Receivable	0.49%	0.83%
Private Education Loans | Interest Rate Reduction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 17,621	$ 23,117
% of Total Class of Financing Receivable	0.09%	0.12%
Private Education Loans | Interest Rate Reduction | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	10.38%	10.36%
Private Education Loans | Interest Rate Reduction | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	4.00%	4.00%
Private Education Loans | Combination - Interest Rate Reduction and Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 96,015	$ 162,049
% of Total Class of Financing Receivable	0.49%	0.83%
Weighted average life of loans	10 years 4 months 2 days	10 years 5 months 1 day
Private Education Loans | Combination - Interest Rate Reduction and Term Extension | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	10.04%	9.80%
Private Education Loans | Combination - Interest Rate Reduction and Term Extension | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	4.00%	4.00%