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Fair Value Accounting (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value Accounting
Other investments	$ 4,838	$ 5,462
Fair Value Transfers Between Levels	0
Midas Gold Shares
Fair Value Accounting
Other investments	4,838	5,462	$ 3,746
Recurring | Midas Gold Shares
Fair Value Accounting
Other investments	4,838	5,462
Recurring | Fair Value, Inputs, Level 1 | Midas Gold Shares
Fair Value Accounting
Other investments	$ 4,838	5,462
Non-recurring | Used mill equipment, Canada
Fair Value Accounting
Used mill equipment (non-recurring)		5,500
Non-recurring | Fair Value, Inputs, Level 3 | Used mill equipment, Canada
Fair Value Accounting
Used mill equipment (non-recurring)		$ 5,500

X

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
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+ References

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- Definition

Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
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- Definition

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+ References

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