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STOCK-BASED COMPENSATION AND EMPLOYEE BENEFIT PLANS (Employee Benefit Plans) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($) employee | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Defined Contribution Plan Disclosure [Line Items] |  |  |
Number of active non-supervisory Canadian employees | employee | 12 |  |
Net periodic benefit cost | $ 0.4 | $ 0.4 | $ 0.3
Pension assets measured at fair value | 9.3 | 8.4 |
Projected benefit obligation | 10.9 | 9.9 |
Level 1 |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Pension assets measured at fair value | 3.9 | 3.5 |
Level 2 |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Pension assets measured at fair value | $ 5.4 | $ 4.9 |

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- Definition Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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