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Significant Accounting Policies (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) item	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (427,918)		$ (426,968)
Mineral income
Number of projects currently in production that could provide NSRs | item	0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit		$ 0
Option Agreement Two [Member] | Guadalupe De Los Reyes, Mexico [Member]
Mineral income
Value of carrying value for option payment proceeds to be recognized as contract liability	$ 0

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- Definition

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(a)(4))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30)(a)(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Represents the number of projects that are currently in production that could provide entity with net smelter return (NSR).

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The amount of the carrying value for the remaining option payment proceeds to be recognized as a contract liability until the title has been transferred to the buyer or the option agreement has been terminated.

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