Income taxes (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2011 | Sep. 30, 2010 | Sep. 30, 2011 | Sep. 30, 2010 | |
| Components Of Income Tax Expense Benefit Continuing Operations [Abstract] | ||||
| Provision for income taxes | $ 20.9 | $ 15.5 | $ 37.9 | $ 46.1 |
| Effective income tax rate | 36.50% | 38.30% | 34.90% | 49.50% |
| U.S. Valuation Allowance Release | 4.4 | 13.9 | ||
| Foreign tax differential | 1.6 | 6.2 | ||
| Benefit related to a tax settlement | $ 7.9 | |||