|**Significant Accounting Policies (Tables)** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
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|**Accounting Policies [Abstract]**           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Property, Plant and Equipment                | The following table shows estimated useful lives of property, plant and equipment:Property, plant and equipmentUseful LifeBuildings40 to 50 yearsLeasehold improvementsLesser of lease term or the life of the assetMachinery, equipment and furniture3 to 10 yearsComputer software5 to 10 yearsThe components of net property, plant and equipment were as follows:December 31,(in millions of dollars)20172016Land and improvements$28.0$18.9Buildings and improvements to leaseholds152.6119.1Machinery and equipment453.5382.0Construction in progress11.18.0645.2528.0Less: accumulated depreciation(366.7)(329.6)Property, plant and equipment, net(1)$278.5$198.4(1)Net property, plant and equipment as ofDecember 31, 2017and2016contained$42.1 millionand$34.7 millionof computer software assets, respectively, which are classified within machinery and equipment and construction in progress. Amortization expense for software was$7.1 million,$7.0 millionand$6.1 millionfor the years endedDecember 31, 2017,2016and2015, respectively.
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|Property, plant and equipment                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Buildings                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Leasehold improvements                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Machinery, equipment and furniture           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|Computer software                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
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|                                             | December 31,                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|(in millions of dollars)                     | 2017                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Land and improvements                        | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Buildings and improvements to leaseholds     | 152.6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Machinery and equipment                      | 453.5                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Construction in progress                     | 11.1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|                                             | 645.2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Less: accumulated depreciation               | (366.7                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Property, plant and equipment, net(1)        | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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|(1)                                          | Net property, plant and equipment as ofDecember 31, 2017and2016contained$42.1 millionand$34.7 millionof computer software assets, respectively, which are classified within machinery and equipment and construction in progress. Amortization expense for software was$7.1 million,$7.0 millionand$6.1 millionfor the years endedDecember 31, 2017,2016and2015, respectively.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            

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