Income Taxes - Uncertain Tax Positions (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Uncertain tax positions: | |||
| Beginning of year | $ 6.4 | $ 6.9 | $ 7.2 |
| Increases related to prior-year tax positions | 0.1 | 0.6 | 0.0 |
| Decreases related to prior-year tax positions | (0.5) | (0.4) | (0.3) |
| Increases related to current-year tax positions | 1.4 | 1.2 | 1.1 |
| Increases related to acquisitions | 4.2 | 0.0 | 0.0 |
| Settlements | (0.1) | (0.8) | 0.0 |
| Effect of the expiration of statutes of limitation | (0.8) | (0.8) | (0.7) |
| Foreign currency exchange effects | (0.3) | (0.3) | (0.4) |
| End of year | $ 10.4 | $ 6.4 | $ 6.9 |