Stock-Based Compensation Unrecognized Compensation Cost (Details) $ in Millions |
Dec. 31, 2017
USD ($)
|
|---|---|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |
| Unrecognized compensation cost | $ 79.9 |
| Stock Awards | |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |
| Unrecognized compensation cost | 39.5 |
| Stock Options | |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |
| Unrecognized compensation cost | $ 40.4 |