v3.5.0.2

Stock-Based Compensation (Tables) | 6 Months Ended
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Jun. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Summary of Share Based Compensation Expense | The table below sets forth the total amount of stock-based compensation expense for the six months and quarters ended June 30, 2016 and 2015.
|  | Quarter Ended |  |  | Six Months Ended |
|  | June 30, |  |  | June 30, |
|  | 2016 |  |  | 2015 |  |  | 2016 |  |  | 2015 |
|  | (Thousands of dollars) |
Stock-based compensation expense: |  |  |  |
Time-based restricted units |  | $ | 597 |  |  | $ | 571 |  |  | $ | 1,216 |  |  | $ | 1,208 |
Performance-based restricted units |  |  | 809 |  |  |  | 1,069 |  |  |  | 1,680 |  |  |  | 2,151 |
Total stock-based compensation expense |  | $ | 1,406 |  |  | $ | 1,640 |  |  | $ | 2,896 |  |  | $ | 3,359 |

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