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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

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UNAUDITED SUPPLEMENTARY QUARTERLY INFORMATION (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Unaudited supplementary quarterly information
Revenues									$ 117,019	$ 128,175	$ 67,465
Gross profit	$ 1,261	$ 1,619	$ 4,677	$ 1,429	$ 2,749	$ 6,013	$ 9,092	$ 14,228	8,986	32,082	20,080
Net loss	$ (25,132)	$ (11,465)	$ (13,014)	$ (10,136)	$ (20,989)	$ (13,290)	$ (5,380)	$ (5,211)	$ (59,747)	$ (44,870)	$ (10,634)
Net (loss) per share:
Basic and diluted (in dollars per share)	$ (0.07)	$ (0.03)	$ (0.04)	$ (0.02)	$ (0.06)	$ (0.04)	$ (0.02)	$ (0.02)	$ (0.17)	$ (0.13)	$ (0.03)
Weighted average shares outstanding:
Basic and diluted (in shares)	378,543	362,175	346,998	345,497	337,936	337,278	337,087	337,062	361,845	337,297	313,887
MSC
Unaudited supplementary quarterly information
Revenues									$ 263,887	$ 213,096	$ 235,650
Gross profit									(33,977)	(9,117)	(31,025)
Net loss									(4,279)	(20,541)	(4,750)
Gold and silver sales
Unaudited supplementary quarterly information
Revenues	$ 32,362	$ 32,691	$ 36,383	$ 15,583	$ 26,432	$ 26,896	$ 33,806	$ 41,041	$ 117,019	$ 128,175	$ 67,465