| **Stock-Based Compensation (Tables)**                                                                                    | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
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| **Disclosure of Compensation Related Costs, Share-based Payments [Abstract]**                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan | The following table summarizes the Company’s stock-based compensation expense (including stock options, restricted stock units (“RSUs”) and performance stock units (“PSUs”)) for the three and nine months ended September 30, 2014 and 2013:Three Months Ended September 30, Nine Months Ended September 30,(in millions of dollars)2014 2013 2014 2013Stock option compensation expense$0.9 $0.8 $2.8 $2.2RSU compensation expense1.4 1.3 5.0 4.4PSU compensation expense1.6 2.2 3.8 5.1Total stock-based compensation$3.9 $4.3 $11.6 $11.7 |
| Schedule of Unrecognized Compensation Cost, Nonvested Awards                                                             | The following table summarizes the Company's unrecognized compensation expense and the weighted-average period over which the expense will be recognized as of September 30, 2014:September 30, 2014Unrecognized Weighted AverageCompensation Years Expense To Be(in millions of dollars, except weighted average years)Expense Recognized OverStock options$5.5 2.0RSUs$6.2 1.9PSUs$9.8 1.8                                                                                                                                                                                                                              |

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| - Definition
Tabular disclosure of the amount of total share-based compensation cost, including the amounts attributable to each share-based compensation plan and any related tax benefits.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901
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| - Definition
Tabular disclosure of the total compensation cost related to nonvested awards not yet recognized and the weighted-average period over which it is expected to be recognized.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901
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