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v3.19.1

Decommissioning Liabilities (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Asset Retirement Obligation Disclosure [Line Items] |  |
Estimated reclamation discount rate | 2.30% | 2.30%
Closure cost obligations discount rate | 8.40% | 7.60%
Bottom of range [member] |  |
Asset Retirement Obligation Disclosure [Line Items] |  |
Inflation rate | 2.00% | 2.00%
Top of range [member] |  |
Asset Retirement Obligation Disclosure [Line Items] |  |
Inflation rate | 4.20% | 4.00%
Provision for decommissioning, restoration and rehabilitation costs [member] |  |
Asset Retirement Obligation Disclosure [Line Items] |  |
Asset retirement obligation, undiscounted value | $ 53.4 | $ 53.2

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- Definition Closure Cost Obligations Discount Rate + References No definition available. + Details
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