Properties, Plant and Equipment (Details) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
|
Jun. 30, 2015
USD ($)
|
Jun. 30, 2014
USD ($)
|
Jun. 30, 2015
USD ($)
a
|
Jun. 30, 2014
USD ($)
|
|
| Property, Plant and Equipment [Abstract] | ||||
| Capital expenditures | $ 3.7 | |||
| Capital expenditures for design and construction of the heap leach expansion and related infrastructure | 1.9 | |||
| Escrow amount closed on purchase of property | $ 1.8 | |||
| Area of properties purchased (in acres) | a | 7.5 | |||
| Depreciation expense | $ 1.6 | $ 1.3 | $ 3.2 | $ 2.7 |