Supplementary Disclosures of Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Non-cash financing and investing activities:
Mining equipment acquired through issuance of debt	$ 5,895	$ 295
Non-cash finder fees	59	0
Mining Properties and Mineral Rights [Member]
Cash paid during the period for:
Interest on loan payable	428	468
Non-cash financing and investing activities:
Asset retirement costs charged to mineral property interests	260	245
Mineral property expenditures included in accounts payable	1,081	318
Interest cost capitalized to mineral property interests	0	839
Non-cash amortization of discount and interest expense	1,250	1,853
Interest payable converted to principal balance	$ 1,560	$ 2,977