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Financial Instruments and Risk Management (Foreign Currency Exchange Rate Risk) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | $ 228.1 | $ 187.5
Unrealized gains | $ (0.7) | 0.6
Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Potential percentage change in value | 10.00% |
Canadian dollar | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | $ 32.6 | 11.7
Impact on pre-tax earnings | 3.3 | 1.2
Mexican peso | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 3.9 | 15.6
Impact on pre-tax earnings | 0.4 | 1.7
Cash and Cash Equivalents [Member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 220.5 | 182.8
Cash and Cash Equivalents [Member] | Canadian dollar | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 33.5 | 22.5
Cash and Cash Equivalents [Member] | Mexican peso | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 6.5 | 9.0
Equity Securities [Member] | Canadian dollar | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 43.7 | 22.8
Equity Securities [Member] | Mexican peso | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 0.0 | 0.0
Trade receivables [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 7.6 | 4.7
Trade receivables [member] | Canadian dollar | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 6.9 | 10.3
Trade receivables [member] | Mexican peso | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 18.7 | 20.9
Other monetary assets [member] | Canadian dollar | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 20.2 | 33.0
Other monetary assets [member] | Mexican peso | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | 4.1 | 3.7
Accounts Payable And Accrued Liabilities [Member] | Canadian dollar | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | (71.7) | (76.9)
Accounts Payable And Accrued Liabilities [Member] | Mexican peso | Currency risk [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | $ (25.4) | $ (18.0)

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