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Stock-Based Compensation Plans and Arrangements - Additional Information (Detail) |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Apr. 30, 2014 USD ($) | Dec. 31, 2015 USD ($) compensation_plan shares | Dec. 31, 2014 USD ($) shares | Dec. 31, 2013 USD ($) 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 |  |  |  |
Incremental expense on vested awards | $ 100,000 |  |  |  |  |
Incremental expense on unvested equity awards | $ 600,000 |  |  |  |  |
Stock-based compensation cost |  | $ 21,598,000 | $ 24,971,000 | $ 15,681,000 |  |
Unrecognized compensation cost |  | $ 14,400,000 |  |  |  |
Weighted average period for total unrecognized compensation cost |  | 1 year 9 months 15 days |  |  |  |
Vesting period |  | 3 years |  |  |  |
Options granted in period (in shares) | shares |  | 0 |  |  |  |
Offering period of employee stock purchase plan |  | 12 months |  |  |  |
Maximum contribution amount per employee to ESPP |  | $ 7,500 |  |  |  |
SLM Corporation 2012 Omnibus Incentive Plan |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Shares authorized to be issued under plan | shares |  | 29,000,000 |  |  |  |
Grants made in 2012 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Maximum term for stock options (in years) |  | 5 years |  |  |  |
Grants made prior to 2012 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Maximum term for stock options (in years) |  | 10 years |  |  |  |
Restricted Stock Units (RSUs) |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Vesting period |  | 3 years |  |  |  |
Performance Vesting Stock Options |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Vesting period |  | 3 years |  |  |  |
Performance Vesting Stock Options | Tranche 1 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Vesting percentage per year of performance-vested options granted to management |  | 33.33% |  |  |  |
Performance Vesting Stock Options | Tranche 2 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Vesting percentage per year of performance-vested options granted to management |  | 33.33% |  |  |  |
Performance Vesting Stock Options | Tranche 3 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Vesting percentage per year of performance-vested options granted to management |  | 33.33% |  |  |  |
Restricted Stock |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Unrecognized compensation cost |  | $ 400,000 |  |  |  |
Weighted average period for total unrecognized compensation cost |  | 6 months |  |  |  |
Vesting period |  | 3 years |  |  |  |
Employee Stock Purchase Plan |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Shares authorized to be issued under plan | shares |  |  |  |  | 15,000,000 | 6,000,000
Unrecognized compensation cost |  | $ 200,000 |  |  |  |
Vesting period |  | 1 year |  |  |  |
Percentage of discount available to employees under ESPP |  | 15.00% |  |  |  |
Expected dividend rate |  | 0.00% | 0.00% | 3.51% |  |
Company's common stock purchased by ESPP participants | shares |  | 163,136 | 0 | 47,176 |  |

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