Stock-Based Compensation - Stock Option Activity (Detail) - Performance-Based Stock Options [Member] |
3 Months Ended |
|---|---|
|
Mar. 31, 2018
$ / shares
shares
| |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |
| Outstanding, Shares Under Option, Beginning of Period | shares | 2,147,562 |
| Granted, Shares Under Option | shares | 0 |
| Outstanding, Shares Under Option, End of Period | shares | 2,147,562 |
| Weighted Average Exercise Price, Beginning of Period | $ / shares | $ 513.50 |
| Granted, Weighted Average Exercise Price | $ / shares | 0 |
| Weighted Average Exercise Price, End of Period | $ / shares | $ 513.50 |