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v3.24.1.u1

Allowance for Credit Losses - Narrative (Details) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2024 USD ($) payment | Dec. 31, 2023 USD ($) | Dec. 31, 2023 USD ($) | Jul. 01, 2006
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing receivable allowance period increase (decrease) | $ (102,000,000) |  |  |
Loan sale reduction to provision | $ 133,204,000 |  |  |
Criteria for loans to be considered as nonperforming (greater than) | 90 days |  |  |
Tier 1 of government guarantee (at least) | 97.00% |  |  | 97.00%
Maximum amount of forbearance granted | 12 months |  |  |
Number of monthly payments required by a borrower between successive grants of forbearance | payment | 12 |  |  |
Interest rate reduction |  | 2.00% |  |
Modified loans | $ 257,752,000 |  | $ 380,526,000 |
Threshold period for payment default | 60 days |  |  |
Period of loans past due that have accrued interest | 90 days |  |  |
Monthly payment that is smaller than the interest accrued on the loan in that month | $ 25 |  |  |
Extended Maturity |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing receivable, troubled debt restructuring, subsequent default, number of contracts | payment | 0 |  |  |
Private Education Loans | Extended Maturity |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financial receivable, excluding accrued interest, modified, accumulated |  | $ 10,500,000 | 10,500,000 |
Financial receivable, excluding accrued interest, modified in period, to total financing receivables, percentage |  | 0.05% |  |
Financing receivable, modified, weighted average term increase from modification |  | 6 years 7 months 6 days |  |
Modified loans | $ 200,000 |  |  |
Financing receivable, troubled debt restructuring, premodification | $ 200,000 |  |  |
Threshold period for payment default | 60 days |  |  |
Loan delinquent 30-59 days |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Modified loans | $ 5,166,000 |  | 17,205,000 |
Loan delinquent 30-59 days | Private Education Loans | Extended Maturity |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financial receivable, excluding accrued interest, modified, accumulated | 400,000 |  |  |
Loan delinquent 60-89 days |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Modified loans | 2,476,000 |  | 7,689,000 |
Loan delinquent 60-89 days | Private Education Loans | Extended Maturity |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financial receivable, excluding accrued interest, modified, accumulated | 80,000.00 |  |  |
Loan delinquent 90 days or greater past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Modified loans | 2,508,000 |  | 13,822,000 |
Loan delinquent 90 days or greater past due | Private Education Loans | Extended Maturity |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financial receivable, excluding accrued interest, modified, accumulated | 200,000 |  |  |
Loan delinquent, current |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Modified loans | 244,289,000 |  | 334,967,000 |
Loan delinquent, current | Private Education Loans | Extended Maturity |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financial receivable, excluding accrued interest, modified, accumulated | 9,800,000 |  |  |
Private Education Loans |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loan sale reduction to provision | 133,204,000 |  |  |
Loans sold | 2,100,000,000 |  |  |
Modified loans | $ 257,752,000 |  | 380,526,000 |
Threshold period when delinquent loans are written off | 120 days |  |  |
Private Education Loans | Loan delinquent 30-59 days |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Modified loans | $ 5,166,000 |  | 17,205,000 |
Private Education Loans | Loan delinquent 60-89 days |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Modified loans | 2,476,000 |  | 7,689,000 |
Private Education Loans | Loan delinquent 90 days or greater past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Modified loans | 2,508,000 |  | 13,822,000 |
Private Education Loans | Loan delinquent, current |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Modified loans | 244,289,000 |  | $ 334,967,000 |
FFELP Loans |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loan sale reduction to provision | $ 0 |  |  |
Percentage of FFELP loans insured and guaranteed (at least) | 97.00% |  |  |
Maximum |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Increments in which forbearance is granted | 2 months |  |  |
Interest rate offered to borrowers facing financial difficulty |  | 8.00% | 8.00% |
Temporary interest rate reduction, period |  | 4 years | 4 years |
Minimum |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Increments in which forbearance is granted | 1 month |  |  |
Interest rate offered to borrowers facing financial difficulty |  | 2.00% | 2.00% |
Temporary interest rate reduction, period |  | 2 years | 2 years |

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