Subsequent Events (Details) - USD ($)	Jul. 31, 2015	Jun. 30, 2015
Employee Severance | Minimum | Subsequent Event
Subsequent Event [Line Items]
Restructuring and related cost, expected cost	$ 500,000.0
Employee Severance | Maximum | Subsequent Event
Subsequent Event [Line Items]
Restructuring and related cost, expected cost	1,000,000
Facility Closing
Subsequent Event [Line Items]
Mine reclamation liability accrued		$ 16,000,000
Facility Closing | Maximum | Subsequent Event
Subsequent Event [Line Items]
Restructuring and Related Cost, Expected Cost Remaining	$ 15,000,000