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Other (Loss) Gain (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Other Gain (Loss) [Abstract] |  |
Reduction of obligation to renounce flow-through exploration expenditures | $ 2.3 | $ 1.3
Unrealized gains on non-hedged derivatives | (0.3) | 1.6
Fair value adjustment on prepayment option embedded derivative | 0.0 | 9.5
Loss on disposal of assets | (1.9) | (4.6)
Interest income | 2.5 | 2.1
Reclamation, care and maintenance | (3.8) | 0.0
Transaction costs | (1.3) | 0.0
Other | 1.9 | (2.3)
Other gains (losses) | $ (0.6) | $ 7.6

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- Definition other nonoperating income (expense) + References No definition available. + Details
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