Allowance for Credit Losses - Amortized Cost Basis of Financing Receivables (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($)
Interest Rate Reduction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 7,679
% of Total Class of Financing Receivable	0.04%
Combination - Interest Rate Reduction and Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 79,597
% of Total Class of Financing Receivable	0.37%
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period when delinquent loans are written off	120 days
Private Education Loans | Interest Rate Reduction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 7,679
% of Total Class of Financing Receivable	0.04%
Private Education Loans | Interest Rate Reduction | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	10.09%
Private Education Loans | Interest Rate Reduction | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	4.00%
Private Education Loans | Combination - Interest Rate Reduction and Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 79,597
% of Total Class of Financing Receivable	0.37%
Weighted average life of loans	10 years 6 months 3 days
Private Education Loans | Combination - Interest Rate Reduction and Term Extension | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	9.43%
Private Education Loans | Combination - Interest Rate Reduction and Term Extension | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	4.00%