Fair Value Measurement - Statement Of Income Classification (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Sales
Fair Value Statement Of Income Classification [Line Items]
Realized/unrealized derivative gain (loss), net	$ (738)	$ 1,837
Other Operating Income (Expense)
Fair Value Statement Of Income Classification [Line Items]
Realized/unrealized gold and silver rounds/bullion gain (loss), net	$ (152)	$ 15

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CC
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998890-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

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Balance Type:	credit
Period Type:	duration