Allowance for Credit Losses and Unfunded Loan Commitments - Amortized Cost Basis of Financing Receivables with Loan Modifications (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Interest Rate Reduction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost Basis	$ 8,532	$ 7,093	$ 16,248	$ 13,195
% of Total Class of Financing Receivable	0.04%	0.03%	0.07%	0.05%
Combination - Interest Rate Reduction and Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost Basis	$ 190,630	$ 134,398	$ 371,829	$ 265,624
% of Total Class of Financing Receivable	0.85%	0.55%	1.65%	1.09%
Private Education Loans \| Interest Rate Reduction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost Basis	$ 8,532	$ 7,093	$ 16,248	$ 13,195
% of Total Class of Financing Receivable	0.04%	0.03%	0.07%	0.05%
Private Education Loans \| Interest Rate Reduction \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	12.42%	12.87%	12.54%	12.98%
Private Education Loans \| Interest Rate Reduction \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	4.25%	4.32%	4.40%	4.35%
Private Education Loans \| Combination - Interest Rate Reduction and Term Extension
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized Cost Basis	$ 190,630	$ 134,398	$ 371,829	$ 265,624
% of Total Class of Financing Receivable	0.85%	0.55%	1.65%	1.09%
Weighted average life of loans	9 years 5 months 19 days	9 years 3 months 25 days	9 years 6 months	9 years 4 months 6 days
Private Education Loans \| Combination - Interest Rate Reduction and Term Extension \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	11.85%	12.29%	11.92%	12.23%
Private Education Loans \| Combination - Interest Rate Reduction and Term Extension \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average contractual rate	2.94%	3.98%	2.94%	3.99%