Property, Plant, Equipment and Mineral Interests (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Cost, Begining Balance			$ 145,401	$ 126,017	$ 126,017
Cost, Additions			25,666		19,384
Cost, Transfers			(8,961)		0
Cost, Disposals			(1,538)		0
Cost, Ending Balance	$ 160,568		160,568		145,401
Accumulated depreciation and depletion, Begining Balance			10,851	2,466	2,466
Accumulated depreciation and depletion, Additions	2,931	$ 2,232	8,429	4,081	8,385
Accumulated depreciation and depletion, Disposals			(282)		0
Accumulated depreciation and depletion, Ending Balance	19,374		19,374		10,851
Carrying values	141,194		141,194		134,550
Land [Member]
Property, Plant and Equipment [Line Items]
Cost, Begining Balance			3,893	110	110
Cost, Additions			69		3,777
Cost, Transfers			0		6
Cost, Disposals			(23)		0
Cost, Ending Balance	3,939		3,939		3,893
Accumulated depreciation and depletion, Begining Balance			0	0	0
Accumulated depreciation and depletion, Additions			0		0
Accumulated depreciation and depletion, Disposals			0		0
Accumulated depreciation and depletion, Ending Balance	0		0		0
Carrying values	3,939		3,939		3,893
Mineral property interest and claims [Member]
Property, Plant and Equipment [Line Items]
Cost, Begining Balance			4,453	4,459	4,459
Cost, Additions			547		0
Cost, Transfers			(58)		(6)
Cost, Disposals			0		0
Cost, Ending Balance	4,942		4,942		4,453
Accumulated depreciation and depletion, Begining Balance			72	0	0
Accumulated depreciation and depletion, Additions			211		72
Accumulated depreciation and depletion, Disposals			0		0
Accumulated depreciation and depletion, Ending Balance	283		283		72
Carrying values	4,659		4,659		4,381
Mine development [Member]
Property, Plant and Equipment [Line Items]
Cost, Begining Balance			42,033	84,798	84,798
Cost, Additions			8,511		0
Cost, Transfers			0		(42,765)
Cost, Disposals			0		0
Cost, Ending Balance	50,544		50,544		42,033
Accumulated depreciation and depletion, Begining Balance			971	654	654
Accumulated depreciation and depletion, Additions			1,805		317
Accumulated depreciation and depletion, Disposals			0		0
Accumulated depreciation and depletion, Ending Balance	2,776		2,776		971
Carrying values	47,768		47,768		41,062
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Cost, Begining Balance			60,202	28,085	28,085
Cost, Additions			8,051		0
Cost, Transfers			0		32,117
Cost, Disposals			(1,344)		0
Cost, Ending Balance	66,909		66,909		60,202
Accumulated depreciation and depletion, Begining Balance			7,128	1,462	1,462
Accumulated depreciation and depletion, Additions			4,676		5,666
Accumulated depreciation and depletion, Disposals			(256)		0
Accumulated depreciation and depletion, Ending Balance	11,548		11,548		7,128
Carrying values	55,361		55,361		53,074
Buildings and infrastructure [Member]
Property, Plant and Equipment [Line Items]
Cost, Begining Balance			28,604	8,565	8,565
Cost, Additions			0		9,391
Cost, Transfers			(36)		10,648
Cost, Disposals			(171)		0
Cost, Ending Balance	28,397		28,397		28,604
Accumulated depreciation and depletion, Begining Balance			2,680	350	350
Accumulated depreciation and depletion, Additions			1,765		2,330
Accumulated depreciation and depletion, Disposals			(26)		0
Accumulated depreciation and depletion, Ending Balance	4,419		4,419		2,680
Carrying values	23,978		23,978		25,924
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Cost, Begining Balance			542	0	0
Cost, Additions			8,488		542
Cost, Transfers			(8,867)		0
Cost, Disposals			0		0
Cost, Ending Balance	163		163		542
Accumulated depreciation and depletion, Begining Balance			0	0	0
Accumulated depreciation and depletion, Additions			0		0
Accumulated depreciation and depletion, Disposals			0		0
Accumulated depreciation and depletion, Ending Balance	0		0		0
Carrying values	163		163		542
Interest capitalized [Member]
Property, Plant and Equipment [Line Items]
Cost, Begining Balance			5,674	0	0
Cost, Additions			0		5,674
Cost, Transfers			0		0
Cost, Disposals			0		0
Cost, Ending Balance	5,674		5,674		5,674
Accumulated depreciation and depletion, Begining Balance			0	$ 0	0
Accumulated depreciation and depletion, Additions			348		0
Accumulated depreciation and depletion, Disposals			0		0
Accumulated depreciation and depletion, Ending Balance	348		348		0
Carrying values	$ 5,326		$ 5,326		$ 5,674