Capital Stock - Preferred Shares Authorized, Issued and Outstanding (Detail) - shares |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Series A Nonvoting Participating Preferred Stock [Member] | ||
| Class of Stock [Line Items] | ||
| Shares authorized, $0.01 par value | 20,000,000 | 20,000,000 |
| Shares issued | 0 | 0 |
| Shares outstanding | 0 | 0 |
| Series B Nonvoting Participating Preferred Stock [Member] | ||
| Class of Stock [Line Items] | ||
| Shares authorized, $0.01 par value | 150,000,000 | 150,000,000 |
| Shares issued | 823,188 | 823,188 |
| Shares outstanding | 823,188 | 823,188 |
| Series C Nonvoting Participating Preferred Stock [Member] | ||
| Class of Stock [Line Items] | ||
| Shares authorized, $0.01 par value | 6,000,000 | 6,000,000 |
| Shares issued | 143,458 | 246,522 |
| Shares outstanding | 143,458 | 246,522 |
| Series D Nonvoting Participating Preferred Stock [Member] | ||
| Class of Stock [Line Items] | ||
| Shares authorized, $0.01 par value | 20,000,000 | 20,000,000 |
| Shares issued | 0 | 0 |
| Shares outstanding | 0 | 0 |