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Stock-Based Compensation Plans and Arrangements - Additional Information (Details) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 USD ($) compensation_plan shares | Dec. 31, 2019 USD ($) shares | Dec. 31, 2018 USD ($) shares | Jun. 25, 2014 shares | May 24, 2012 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Number of active stock-based compensation plans | compensation_plan | 1 |  |  |  |
Stock-based compensation cost | $ 36,464,000 | $ 30,600,000 | $ 31,524,000 |  |
Unrecognized compensation cost | $ 17,000,000 |  |  |  |
Weighted average period for total unrecognized compensation cost | 1 year 4 months 24 days |  |  |  |
Vesting period | 3 years |  |  |  |
Options granted in period (in shares) | shares | 0 | 0 | 0 |  |
Offering period of employee stock purchase plan | 12 months |  |  |  |
Maximum contribution amount per employee to ESPP | $ 7,500 |  |  |  |
Employee Stock Purchase Plan |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares authorized to be issued under plan (in shares) | shares |  |  |  | 15,000,000 | 6,000,000
Unrecognized compensation cost | $ 1,000,000 |  |  |  |
Percentage of discount available to employees under ESPP | 15.00% |  |  |  |
Expected dividend rate | 1.76% | 1.34% | 0.00% |  |
Company's common stock purchased by ESPP participants (in shares) | shares | 0 | 0 | 233,232 |  |
Grants made prior to 2012 |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Maximum term for stock options | 10 years |  |  |  |
Performance Vesting Stock Options |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period | 3 years |  |  |  |
Restricted Stock |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Unrecognized compensation cost | $ 1,000,000 |  |  |  |
Weighted average period for total unrecognized compensation cost | 6 months |  |  |  |
Vesting period | 1 year |  |  |  |
Restricted Stock Units (RSUs) |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period | 3 years |  |  |  |
SLM Corporation 2012 Omnibus Incentive Plan |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares authorized to be issued under plan (in shares) | shares | 13,000,000 |  |  |  |

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