| **Stock-Based Compensation**                                                  | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
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| **Disclosure of Compensation Related Costs, Share-based Payments [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Stock-Based Compensation                                                      | 6. Stock-Based CompensationThe following table summarizes our stock-based compensation expense (including stock options, restricted stock units ("RSUs") and performance stock units ("PSUs")) for the three and six months ended June 30, 2016 and 2015:Three Months Ended June 30, Six Months Ended June 30,(in millions of dollars)2016 2015 2016 2015Stock option compensation expense$0.7 $1.0 $1.6 $1.9RSU compensation expense1.6 1.6 2.6 2.8PSU compensation expense2.3 2.0 3.7 2.9Total stock-based compensation expense$4.6 $4.6 $7.9 $7.6During the second quarter of 2016, the Company's Board of Directors approved the annual stock compensation grant to eligible non-employee directors, which consisted of 9,128 shares of stock (included in RSU compensation expense) and 73,024 RSUs.Also during the second quarter of 2016, the Company's Board of Directors approved employee stock compensation grants, which consisted of 3,098 RSUs and 7,333 PSUs.We generally recognize compensation expense for stock-based awards ratably over the vesting period. Stock-based compensation expense for the three and six months ended June 30, 2016 and 2015 includes $0.8 million and $0.8 million, respectively, of expense related to stock awards granted to eligible non-employee directors, which were fully vested on the grant date.The following table summarizes our unrecognized compensation expense and the weighted-average period over which the expense will be recognized as of June 30, 2016:June 30, 2016Unrecognized Weighted AverageCompensation Years Expense To Be(in millions of dollars, except weighted average years)Expense Recognized OverStock options$3.0 1.3RSUs$5.3 2.0PSUs$11.4 2.0 |

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| - Definition
The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.
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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 40 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 50 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=51659978&loc=d3e25284-112666Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5444-113901Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14
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| - References
No definition available.
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