v3.7.0.1

Stock-Based Compensation (Tables) | 3 Months Ended
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Mar. 31, 2017
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 quarters ended March 31, 2017 and 2016.
|  | Quarter Ended |
|  | March 31, |
|  | 2017 |  |  | 2016 |
|  | (Thousands of dollars) |
Stock-based compensation expense: |  |  |  |
Time-based restricted stock units |  | $ | 553 |  |  | $ | 619 |
Performance-based restricted stock units |  |  | — |  |  |  | 871 |
Total stock-based compensation expense |  | $ | 553 |  |  | $ | 1,490 |

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