Impairment of Goodwill (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Mar. 31, 2015
Goodwill
Impairment of goodwill	$ 11,666
Velardena Properties
Goodwill
Discount rate (as a percent)	21.00%
Velardena Properties | Expected results
Goodwill
Expected plant throughput (in tonnes per day)		285
Velardena Properties | Silver | Maximum
Goodwill
Metal prices used in analysis (in dollars per ounce)	23.80
Velardena Properties | Silver | Minimum
Goodwill
Metal prices used in analysis (in dollars per ounce)	18.06
Velardena Properties | Gold | Maximum
Goodwill
Metal prices used in analysis (in dollars per ounce)	1,440
Velardena Properties | Gold | Minimum
Goodwill
Metal prices used in analysis (in dollars per ounce)	1,198