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Management of Financial Risk (Disclosure of Nature and Extent Arising from Financial Instruments - Commodity Price Risk) (Details) - Commodity price risk [member] $ in Thousands | 12 Months Ended
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Dec. 31, 2018 USD ($) $ / T T
Gold Commodity Type [member] |
Disclosure of nature and extent of risks arising from financial instruments [line items] |
Effect on Sales | $ 1,332
Change percentage, commodity | 10.00%
Silver Commodity Type [member] |
Disclosure of nature and extent of risks arising from financial instruments [line items] |
Effect on Sales | $ 2,201
Change percentage, commodity | 10.00%
Lead Commodity [member] |
Disclosure of nature and extent of risks arising from financial instruments [line items] |
Effect on Sales | $ 196
Change percentage, commodity | 10.00%
Zinc Commodity [member] |
Disclosure of nature and extent of risks arising from financial instruments [line items] |
Effect on Sales | $ 365
Change percentage, commodity | 10.00%
Aggregate quantity of zero cost collars | T | 4,500
Floor Price | $ / T | 3,050
Cap Price | $ / T | 3,300

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- Definition Aggregate quantity of zero cost collars. + References No definition available. + Details
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Namespace Prefix: | fsm_
Data Type: | num:weightItemType
Balance Type: | na
Period Type: | instant

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- Definition Cap price per tonne. + References No definition available. + Details
Name: | fsm_CapPrice
Namespace Prefix: | fsm_
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Balance Type: | na
Period Type: | instant

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- Definition Floor price per tonne. + References No definition available. + Details
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Namespace Prefix: | fsm_
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Balance Type: | na
Period Type: | instant

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- Definition Percentage change on commodity price percentage. + References No definition available. + Details
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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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- Details
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Namespace Prefix: |
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Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |