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Mineral Property, Pland and Equipment (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Disclosure of detailed information about property, plant and equipment [line items]
Construction in progress		$ 64.4	$ 52.5
Interest costs capitalised		$ 2.0	$ 6.6
Capitalisation rate of borrowing costs eligible for capitalisation		8.62%	8.62%
Royalty Rights [Member]
Disclosure of detailed information about property, plant and equipment [line items]
Additions other than through business combinations, property, plant and equipment	$ 6.7

X

- Definition

The amount of additions to property, plant and equipment other than those acquired through business combinations. [Refer: Business combinations [member]; Property, plant and equipment]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 16
-IssueDate 2017-01-01
-Paragraph 73
-Subparagraph e
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=16&date=2017-03-01&anchor=para_73_e_i&doctype=Standard
-URIDate 2017-03-09

+ Details

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Period Type:	duration

X

- Definition

The weighted average of interest and other costs that an entity incurs in connection with the borrowing of funds applicable to the borrowings of the entity that are outstanding during the period, other than borrowings made specifically for the purpose of obtaining a qualifying asset. [Refer: Weighted average [member]; Borrowings]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 23
-IssueDate 2017-01-01
-Paragraph 26
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=23&date=2017-03-01&anchor=para_26_b&doctype=Standard
-URIDate 2017-03-09

+ Details

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X

- Definition

The amount of expenditure capitalised during the construction of non-current assets that are not yet available for use. [Refer: Non-current assets]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 16
-IssueDate 2017-01-01
-Paragraph 37
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=16&date=2017-03-01&anchor=para_37&doctype=Standard
-URIDate 2017-03-09

+ Details

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X

- 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.

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X

- Definition

The amount of interest costs that an entity incurs in connection with the borrowing of funds that are directly attributable to the acquisition, construction or production of a qualifying asset and which form part of the cost of that asset.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2017-03-09

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X

- Details

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