Property, Plant and Equipment, Net - Disposals (Details) - USD ($)	1 Months Ended			3 Months Ended			9 Months Ended
	Sep. 30, 2018	Feb. 28, 2018	Aug. 31, 2016	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Oct. 31, 2018
Property, plant and equipment
Proceeds from sale of assets							$ 144,000	$ 4,699,000
Gain on sale of assets							144,000	4,335,000
Celaya | Sale, not discontinued operations
Property, plant and equipment
Proceeds from sale of assets			$ 200,000
Gain on sale of assets								1,000,000
Interest in joint venture (as a percent)		20.00%	40.00%
Exploration expenditures in first three year of the agreement			$ 2,500,000
Initial term of agreement			3 years
Term of second agreement		3 years	3 years
Net profit interest		10.00%
Celaya | Sale, not discontinued operations | Execution of Assignment Agreement
Property, plant and equipment
Gain on sale of assets								$ 3,000,000
Celaya | Electrum | Sale, not discontinued operations
Property, plant and equipment
Earn-in to be received	$ 3,000,000	$ 1,000,000	$ 500,000
Interest in joint venture (as a percent)	100.00%	80.00%	60.00%	100.00%				100.00%
Exploration expenditures in first three year of the agreement			$ 2,500,000
Additional interest in joint venture (as a percent)		20.00%
Exploration expenditures in second three year of the agreement		$ 2,500,000
Contribution from additional expenditures required in the second three-year earn-in period (as a percent)		100.00%
Zacatecas | Sale, not discontinued operations
Property, plant and equipment
Proceeds from sale of assets				$ 212,000	$ 225,000	$ 249,000
Gain on sale of assets								$ 336,000
Total consideration			$ 1,500,000				$ 1,500,000
Receivable from sale									$ 13,000
Zacatecas | Sale, not discontinued operations | Other current liabilities [Member]
Property, plant and equipment
Unearned performance obligation	$ 225,000			$ 225,000				$ 225,000