Fair Value Measurements - Schedule of Fair Value of Long-term Borrowings (Detail) - USD ($) $ in Thousands |
Jun. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Long-term Borrowings: | ||
| Carrying amount of senior notes | $ 304,489 | $ 303,416 |
| 5.0% Exchangeable Senior Notes due March 2021 [Member] | Exchangeable Senior Notes [Member] | Significant Other Observable Inputs (Level 2) [Member] | ||
| Long-term Borrowings: | ||
| Carrying amount of senior notes | 82,249 | 81,576 |
| Estimated fair value of senior notes | 131,100 | 127,617 |
| 6.625% Senior Notes Due 2021 [Member] | Senior Notes [Member] | Significant Other Observable Inputs (Level 2) [Member] | ||
| Long-term Borrowings: | ||
| Carrying amount of senior notes | 222,240 | 221,840 |
| Estimated fair value of senior notes | $ 218,700 | $ 224,719 |