Mineral Properties and Mine Development (Schedule of Mineral Properties) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Mining Properties, Mineral Rights and Mine Development [Member]
Property, Plant and Equipment [Line Items]
Mineral properties and mine development, gross	$ 1,075,053	$ 1,030,542
Accumulated depletion and amortization	(489,190)	(457,311)
Total mineral properties and mine development, net	585,863	573,231
Montana, United States of America [Member] | Mining Properties and Mineral Rights [Member] | Stillwater Mine [Member]
Property, Plant and Equipment [Line Items]
Mineral properties and mine development, gross	1,950	1,950
Montana, United States of America [Member] | Mine Development [Member] | Stillwater Mine [Member]
Property, Plant and Equipment [Line Items]
Mineral properties and mine development, gross	735,009	697,781
Montana, United States of America [Member] | Mine Development [Member] | East Boulder Mine [Member]
Property, Plant and Equipment [Line Items]
Mineral properties and mine development, gross	227,564	220,281
Ontario, Canada [Member] | Mining Properties and Mineral Rights [Member] | Marathon Property [Member]
Property, Plant and Equipment [Line Items]
Mineral properties and mine development, gross	8,560	8,560
San Juan, Argentina [Member] | Mining Properties and Mineral Rights [Member] | Altar Property [Member]
Property, Plant and Equipment [Line Items]
Mineral properties and mine development, gross	$ 101,970	$ 101,970