v3.4.0.3

Stock-Based Compensation (Tables) | 3 Months Ended
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Mar. 31, 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 three months and quarters ended March 31, 2016 and 2015.
|  | Quarter Ended March 31, |
|  | 2016 |  |  | 2015 |
Stock-based compensation expense: |  |  | (Thousands of dollars) |
Time-based restricted stock units |  | $ | 619 |  |  | $ | 637 |
Performance-based restricted stock units |  |  | 871 |  |  |  | 1,082 |
Total stock-based compensation expense |  | $ | 1,490 |  |  | $ | 1,719 |

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