v3.8.0.1

Stock-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 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 the nine months and quarter ended September 30, 2017 and 2016.
|  | Quarter Ended September 30, |  | Nine Months Ended September 30,
|  | 2017 |  | 2016 |  | 2017 |  | 2016
|  | (Thousands of dollars)
Stock-based compensation expense: |  |  |  |  |  |
Time-based restricted stock units |  | $ | 582 |  |  | $ | 631 |  |  | $ | 1,678 |  |  | $ | 1,847 |
Performance-based restricted stock units |  | 689 |  |  | 823 |  |  | 1,396 |  |  | 2,502 |
Total stock-based compensation expense |  | $ | 1,271 |  |  | $ | 1,454 |  |  | $ | 3,074 |  |  | $ | 4,349 |

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