Allowance for Credit Losses and Unfunded Loan Commitments - Payment Status (Amortized Cost Basis) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, ,modified in period, amount	$ 1,001,410	$ 373,683
Financing receivable, modified in period, to total financing receivables, percentage	100.00%	100.00%
Amortization cost basis	$ 40,400	$ 8,400
Loan Deferment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, ,modified in period, amount	33,645	6,843
Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, ,modified in period, amount	$ 826,007	$ 334,967
Financing receivable, modified in period, to total financing receivables, percentage	83.00%	90.00%
30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, ,modified in period, amount	$ 77,446	$ 17,205
Financing receivable, modified in period, to total financing receivables, percentage	8.00%	4.00%
60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, ,modified in period, amount	$ 43,484	$ 7,689
Financing receivable, modified in period, to total financing receivables, percentage	4.00%	2.00%
90 Days or Greater Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, ,modified in period, amount	$ 54,473	$ 13,822
Financing receivable, modified in period, to total financing receivables, percentage	5.00%	4.00%
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, ,modified in period, amount	$ 1,035,055	$ 380,526
Amortization cost basis	$ 40,400