Stock-Based Compensation - Summary of Share Based Compensation Expense (Detail) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
|
| Stock-based compensation expense: | ||||
| Total stock-based compensation expense | $ 1,271 | $ 1,454 | $ 3,074 | $ 4,349 |
| Time-based Restricted Units [Member] | ||||
| Stock-based compensation expense: | ||||
| Total stock-based compensation expense | 582 | 631 | 1,678 | 1,847 |
| Performance-based Restricted Units [Member] | ||||
| Stock-based compensation expense: | ||||
| Total stock-based compensation expense | $ 689 | $ 823 | $ 1,396 | $ 2,502 |