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Financial Instruments and Risk Management (Foreign Currency Exchange Rate Risk) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Total financial instrument exposure to credit risk | $ 187.5 | $ 214.0
Unrealized gains | $ 0.6 | 0.4
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 | $ 11.7 | 10.4
Impact on pre-tax earnings | 1.2 | 1.4
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 | 15.6 | 21.3
Impact on pre-tax earnings | 1.7 | 2.1
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 | 182.8 | 206.0
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 | 22.5 | 26.8
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 | 9.0 | 10.8
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 | 22.8 | 7.8
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 | 4.7 | 5.7
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 | 10.3 | 11.9
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 | 20.9 | 21.4
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 | 33.0 | 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 | 3.7 | 5.9
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 | (76.9) | (69.1)
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 | $ (18.0) | $ (16.8)

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