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Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Environmental Contingency |  |  |  |
Environmental accrual increased during the period | $ 3.8 |  |  |
Environmental accrual | $ 18.7 | $ 17.0 | $ 16.9 | $ 16.6
Expected period related to remediation expenditures for environmental contingencies period | 30 years |  |  |
Potential increase in environmental costs | $ 11.6 |  |  |
Time period within which recorded estimate of its obligation may change | 12 months |  |  |
Minimum |  |  |  |
Environmental Contingency |  |  |  |
Period for final feasibility study | 10 months |  |  |
Maximum |  |  |  |
Environmental Contingency |  |  |  |
Period for final feasibility study | 16 months |  |  |
Weighted-average Credit-adjusted Risk-free Rate |  |  |  |
Environmental Contingency |  |  |  |
Weighted-average credit-adjusted risk-free rate (percent) | 8.70% | 8.70% |  |

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