Allowance for Credit Losses - Payment Status (Amortized Cost Basis) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)	$ 9,467	$ 12,660
Deferment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		5,575
Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		236,477
30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		10,335
60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		5,835
90 Days or Greater Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		4,431
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)	$ 9,467	12,660
Private Education Loans | Deferment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		5,575
Private Education Loans | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		236,477
Private Education Loans | 30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		10,335
Private Education Loans | 60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		5,835
Private Education Loans | 90 Days or Greater Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment Status (Amortized Cost Basis)		$ 4,431