Capital Stock - Preferred Shares Authorized, Issued and Outstanding (Parenthetical) (Detail) - $ / shares |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Series A Nonvoting Participating Preferred Stock [Member] | ||
| Class of Stock [Line Items] | ||
| Preferred stock, par value | $ 0.01 | $ 0.01 |
| Series B Nonvoting Participating Preferred Stock [Member] | ||
| Class of Stock [Line Items] | ||
| Preferred stock, par value | 0.01 | 0.01 |
| Series C Nonvoting Participating Preferred Stock [Member] | ||
| Class of Stock [Line Items] | ||
| Preferred stock, par value | 0.01 | 0.01 |
| Series D Nonvoting Participating Preferred Stock [Member] | ||
| Class of Stock [Line Items] | ||
| Preferred stock, par value | $ 0.01 | $ 0.01 |