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Commitments and Contingencies, Environmental (Details) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 USD ($) | Jun. 30, 2018 USD ($)
Environmental Contingency |  |
Environmental accrual | $ 16.5 | $ 16.5
Expected period related to remediation expenditures for environmental contingencies period |  | 30 years
Potential increase in environmental costs | $ 12.2 | $ 12.2
Time period within which Companys recorded estimate of its obligation may change | 12 months |
Minimum |  |
Environmental Contingency |  |
Period for final feasibility study |  | 12 months
Maximum |  |
Environmental Contingency |  |
Period for final feasibility study |  | 18 months

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