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Financial Instruments and Risk Management (Currency Contracts) (Details) MXN in Millions, CAD in Millions, $ in Millions | 12 Months Ended |
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Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2017 CAD | Dec. 31, 2017 USD ($) | Dec. 31, 2017 MXN | Dec. 31, 2017 MXN / $ | Dec. 31, 2017 $ / CAD
Disclosure of detailed information about hedged items [line items] |  |  |  |  |  |  |
Financial assets, at fair value |  |  |  | $ 0.4 |  |  |
Financial liabilities, at fair value |  | $ 2.4 |  |  |  |  |
Gains (losses) on change in fair value of derivatives | $ 2.3 | 1.6 |  |  |  |  |
Collars and Forwards [Member] |  |  |  |  |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |  |  |  |  |
Financial assets, at fair value |  |  |  | $ 5.0 |  |  |
Financial liabilities, at fair value |  | 3.3 |  |  |  |  |
Gains (losses) on change in fair value of derivatives | $ 4.3 | $ (1.6) |  |  |  |  |
2018 [member] | Collars and Forwards [Member] | Currency risk [member] |  |  |  |  |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |  |  |  |  |
Notional amount |  |  | CAD 174 |  | MXN 1,560.0 |  |
Bottom of range [member] | 2018 [member] | Collars and Forwards [Member] | Currency risk [member] |  |  |  |  |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |  |  |  |  |
Average rate of hedging instrument |  |  |  |  |  | 1872.00% | 131.00%
Top of range [member] | 2018 [member] | Collars and Forwards [Member] | Currency risk [member] |  |  |  |  |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |  |  |  |  |
Average rate of hedging instrument |  |  |  |  |  | 2071.00% | 136.00%

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- Definition The average rate of a hedging instrument. [Refer: Hedging instruments [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2018-01-01 -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 23B -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_23B_b&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The fair value of financial assets. [Refer: At fair value [member]; Financial assets] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 25 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_25&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The gains (losses) resulting from change in the fair value of derivatives recognised in profit or loss. [Refer: Derivatives [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 85 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_85&doctype=Standard -URIDate 2017-03-09 + Details
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