Allowance for Credit Losses and Unfunded Loan Commitments - Allowance and Recorded Investments in Loans (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | 12 Months Ended | |||||
|---|---|---|---|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
Dec. 31, 2025 |
Mar. 31, 2026 |
Mar. 31, 2025 |
Dec. 31, 2024 |
|
| Allowance For Credit Losses [Abstract] | ||||||||
| Allowance for loan losses, beginning balance | $ 1,430,318 | |||||||
| Loan sale reduction to provision | $ (116,000) | |||||||
| Net charge-offs: | ||||||||
| Allowance for loan losses, ending balance | $ 1,354,014 | 1,354,014 | $ 1,430,318 | |||||
| Allowance | ||||||||
| Beginning balance | 23,754 | $ 23,890 | 77,132 | 84,568 | 84,568 | |||
| Provision | 70,470 | 56,529 | 116,386 | 100,985 | ||||
| Transfer to allowance for loan losses | (28,209) | (27,878) | (127,503) | (133,012) | ||||
| Ending balance | 66,015 | 52,541 | 66,015 | 52,541 | 77,132 | |||
| Accrued interest to be capitalized | ||||||||
| Unfunded loan commitments for loans held for investment | 1,728,478 | 1,358,163 | 1,728,478 | 1,358,163 | 2,437,035 | $ 587,882 | $ 584,140 | $ 2,311,660 |
| Total accrued interest receivable | 1,602,311 | 1,602,311 | 1,562,811 | |||||
| Private Education Loans | ||||||||
| Allowance For Credit Losses [Abstract] | ||||||||
| Allowance for loan losses, beginning balance | 1,383,166 | 1,443,715 | 1,430,318 | 1,435,920 | 1,435,920 | |||
| Transfer from allowance for unfunded loan commitments | 28,209 | 27,878 | 127,503 | 133,012 | ||||
| Provision for current period | 68,330 | 92,189 | 141,526 | 187,478 | ||||
| Loan sale reduction to provision | (10,826) | (130,912) | (116,459) | |||||
| Loans transferred to held for sale | (2,311) | (12,803) | ||||||
| Total provisions | 55,193 | 92,189 | (2,189) | 71,019 | ||||
| Net charge-offs: | ||||||||
| Charge-offs | (122,216) | (106,866) | (225,049) | (193,769) | ||||
| Recoveries | 9,662 | 12,593 | 23,431 | 23,327 | ||||
| Net charge-offs | (112,554) | (94,273) | (201,618) | (170,442) | ||||
| Allowance for loan losses, ending balance | 1,354,014 | 1,469,509 | 1,354,014 | 1,469,509 | 1,430,318 | |||
| Allowance | ||||||||
| Beginning balance | 23,754 | 23,890 | 77,132 | 84,568 | 84,568 | |||
| Provision | 70,470 | 56,529 | 116,386 | 100,985 | ||||
| Transfer to allowance for loan losses | (28,209) | (27,878) | (127,503) | (133,012) | ||||
| Ending balance | 66,015 | 52,541 | 66,015 | 52,541 | $ 77,132 | |||
| Total allowance for credit losses, ending balance | $ 1,420,029 | $ 1,522,050 | $ 1,420,029 | $ 1,522,050 | ||||
| Accrued interest to be capitalized | ||||||||
| Net charge-offs as a percentage of average loans in repayment (annualized) | 2.95% | 2.36% | 2.55% | 2.11% | ||||
| Allowance coverage of net charge-offs (annualized) | 3.01 | 3.90 | 3.36 | 4.31 | ||||
| Total Allowance Percentage of Private Education Loan Exposure | 5.89% | 5.95% | 5.89% | 5.95% | ||||
| Ending total loans, gross | $ 20,791,497 | $ 22,525,817 | $ 20,791,497 | $ 22,525,817 | ||||
| Average loans in repayment | 15,287,312 | 15,991,357 | 15,786,152 | 16,146,239 | ||||
| Ending loans in repayment | 15,366,596 | 16,231,194 | 15,366,596 | 16,231,194 | ||||
| Unfunded loan commitments for loans held for investment | 1,700,089 | 1,358,163 | 1,700,089 | 1,358,163 | ||||
| Total accrued interest receivable | 1,604,848 | 1,701,944 | 1,604,848 | 1,701,944 | ||||
| Provisions for loan losses | 55,193 | 92,189 | (2,189) | 71,019 | ||||
| Provisions for unfunded loan commitments | 70,470 | 56,529 | 116,386 | 100,985 | ||||
| Provisions for credit losses reported in consolidated statements of income | $ 125,663 | $ 148,718 | 114,197 | $ 172,004 | ||||
| Unfunded loan held-for-sale | $ 28,000 | |||||||