Stock-Based Compensation Unrecognized Compensation Cost (Detail) - USD ($) $ in Millions |
Mar. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Unrecognized compensation cost | $ 115.0 | $ 85.6 |
| Stock Awards | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Unrecognized compensation cost | 60.1 | 43.3 |
| Stock Options | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Unrecognized compensation cost | $ 54.9 | $ 42.3 |