Reclamation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Asset retirement obligation
Asset retirement obligation - Beginning	$ 101,127	$ 85,545	$ 97,380	$ 82,072
Accretion	2,455	2,059	7,190	6,027
Additions and changes in estimates	3,116	(239)	3,116	(118)
Settlements	(656)	(183)	(1,644)	(799)
Asset retirement obligation - Ending	106,042	87,182	106,042	87,182
Property, Plant and Equipment [Line Items]
Additions and changes in estimates	3,116	$ (239)	3,116	$ (118)
Accrued reclamation liabilities	2,100		$ 2,100		$ 1,900
Rochester [Member]
Asset retirement obligation
Additions and changes in estimates	3,100
Property, Plant and Equipment [Line Items]
Additions and changes in estimates	$ 3,100