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Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Detail) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Earning assets: |  |
Trading investments | $ 53,262 | $ 54,481
Accrued interest receivable, difference | 116,884 | 68,862
Derivative instruments | 0 | 0
Total earning assets, difference | 3,325,107 | 2,534,325
Interest-bearing liabilities: |  |
Long-term borrowings, difference | 116,961 | 353,822
Derivative instruments | 40 | 370
Total interest-bearing liabilities, difference | 86,316 | 489,912
Excess of net asset fair value over carrying value | 3,411,423 | 3,024,237
Money-market and savings accounts |  |
Interest-bearing liabilities: |  |
Deposits, difference | 22,593 | 68,409
Certificates of deposit |  |
Interest-bearing liabilities: |  |
Deposits, difference | (53,238) | 67,681
Fair Value |  |
Earning assets: |  |
Cash and cash equivalents | 4,700,366 | 4,149,838
Trading investments | 53,262 | 54,481
Available-for-sale investments | 1,933,226 | 2,411,622
Accrued interest receivable | 1,663,474 | 1,448,766
Derivative instruments | 0 | 0
Total | 32,460,709 | 30,836,527
Interest-bearing liabilities: |  |
Long-term borrowings | 6,323,384 | 4,873,690
Accrued interest payable | 108,488 | 105,066
Derivative instruments | 40 | 370
Total interest-bearing liabilities | 27,529,309 | 26,494,693
Fair Value | Money-market and savings accounts |  |
Interest-bearing liabilities: |  |
Deposits | 10,503,731 | 11,134,883
Fair Value | Certificates of deposit |  |
Interest-bearing liabilities: |  |
Deposits | 10,593,666 | 10,380,684
Carrying Value |  |
Earning assets: |  |
Cash and cash equivalents | 4,700,366 | 4,149,838
Trading investments | 53,262 | 54,481
Available-for-sale investments | 1,933,226 | 2,411,622
Accrued interest receivable | 1,546,590 | 1,379,904
Derivative instruments | 0 | 0
Total | 29,135,602 | 28,302,202
Interest-bearing liabilities: |  |
Long-term borrowings | 6,440,345 | 5,227,512
Accrued interest payable | 108,488 | 105,066
Derivative instruments | 40 | 370
Total interest-bearing liabilities | 27,615,625 | 26,984,605
Carrying Value | Money-market and savings accounts |  |
Interest-bearing liabilities: |  |
Deposits | 10,526,324 | 11,203,292
Carrying Value | Certificates of deposit |  |
Interest-bearing liabilities: |  |
Deposits | 10,540,428 | 10,448,365
Private Education Loans |  |
Earning assets: |  |
Loans held for investment, net, difference | 3,208,223 | 2,456,752
Private Education Loans | Fair Value |  |
Earning assets: |  |
Private Education Loans | 24,110,381 | 22,229,045
Private Education Loans | Carrying Value |  |
Earning assets: |  |
Private Education Loans | 20,902,158 | 19,772,293
FFELP Loans |  |
Earning assets: |  |
Loans held for investment, net, difference | 0 | 8,711
FFELP Loans | Fair Value |  |
Earning assets: |  |
Private Education Loans | 0 | 542,775
FFELP Loans | Carrying Value |  |
Earning assets: |  |
Private Education Loans | $ 0 | $ 534,064

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