Earnings (Loss) per Share - Schedule of Computation of Basic and Diluted Earnings Per Common Share (Parenthetical) (Detail) |
Jun. 30, 2018 |
Dec. 31, 2017 |
Jan. 17, 2017 |
|---|---|---|---|
| 5.0% Exchangeable Senior Notes due March 2021 [Member] | Exchangeable Senior Notes [Member] | |||
| Earnings Per Share [Line Items] | |||
| Conversion of exchangeable notes to common stock rate | 5.00% | 5.00% | 5.00% |