Property, Plant and Equipment, Net - Disposals (Details)			1 Months Ended			3 Months Ended			9 Months Ended
	May 02, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)	Feb. 28, 2018 USD ($)	Aug. 31, 2016 USD ($) item	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Oct. 31, 2018 USD ($)
Property, plant and equipment
Proceeds from sale of asset									$ 4,699,000	$ 750,000
Gain on sale of assets									4,335,000	605,000
Sale, not discontinued operations | Sale of Equipment
Property, plant and equipment
Number of haul trucks sold | item					2
Number of scoop trams sold | item					2
Sale of mining equipments		$ 185,000			$ 687,000
Proceeds from sale of asset	$ 750,000	$ 100,000			$ 69,000
Sales price received (as a percent)					10.00%
Related party receivable					$ 618,000
Interest rate on receivable (as a percent)		10.00%			10.00%
Gain on sale of assets										$ 105,000
Celaya | Sale, not discontinued operations
Property, plant and equipment
Proceeds from sale of asset					$ 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 asset						$ 212,000	$ 225,000	$ 249,000
Gain on sale of assets									$ 523,000
Total consideration			$ 1,500,000		$ 1,500,000	1,500,000			1,500,000
Unearned performance obligation			225,000			225,000			225,000
Receivable from sale											$ 13,000
Expected recognition			$ 225,000			$ 225,000			$ 225,000