Allowance for Credit Losses - Amortized Cost Basis of Financing Receivables that Subsequently Defaulted (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)	$ 326,116
60 Days or Greater Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)	22,925
Payment Default	22,621
Combination - Interest Rate Reduction and Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)	20,600
Interest Rate Reduction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)	2,300
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)	326,116
Private Education Loans | 60 Days or Greater Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)	22,925
Payment Default	$ 22,621