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Financial Instruments and Risk Management (Equity Securities) (Details) $ / shares in Units, $ in Millions |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Feb. 09, 2017 $ / shares | Dec. 31, 2018 USD ($) $ / shares | Mar. 31, 2018 $ / shares | Mar. 31, 2018 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 $ / shares
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Share price (cad per share) | (per share) | $ 7.95 | $ 6.44 |  |  |  | $ 9.40
Proceeds from sales of investment property |  |  |  |  | $ 1.8 |
Monarques Gold Corp [Member] |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Financial assets available-for-sale |  | $ 7.3 |  |  | 7.3 |
Other Investments [Member] |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Financial assets available-for-sale |  | $ 0.5 |  |  | $ 0.5 |
AuRico Metals [Member] |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Share price (cad per share) | $ / shares |  |  | $ 1.80 |  |  |
Proceeds from sales of investment property |  |  |  | $ 22.2 |  |
Gains on disposals of investments |  |  |  | 13.7 |  |
Investment cost per share (cad per share) | $ / shares |  |  | 0.72 |  |  |
Corex Gold Corp [Member] |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Share price (cad per share) | $ / shares |  |  | 0.13 |  |  |
Proceeds from sales of investment property |  |  |  | 2.7 |  |
Gains on disposals of investments |  |  |  | $ 0.6 |  |
Investment cost per share (cad per share) | $ / shares |  |  | $ 0.10 |  |  |

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- Definition The amount of non-derivative financial assets that are designated as available for sale or are not classified as (a) loans and receivables; (b) held-to-maturity investments; or (c) financial assets at fair value through profit or loss. [Refer: Derivative financial assets; Financial assets at fair value through profit or loss; Held-to-maturity investments] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2021-01-01 -Name IFRS -Number 7 -IssueDate 2018-01-01 -Paragraph 8 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_8_d&doctype=Standard&book=b -URIDate 2018-03-16 + Details
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- Definition The cash inflow from sales of investment property. [Refer: Investment property] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 7 -IssueDate 2018-01-01 -Paragraph 16 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2018-03-01&anchor=para_16&doctype=Standard -URIDate 2018-03-16 + Details
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