Commitments and Contingencies (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Dec. 31, 2013
Cote Blanche [Member]    
Loss Contingencies [Line Items]    
Reserve for expected payments required to resolve the dispute   $ 5
Additional amount of reserve for expected payments required to resolve the dispute 2  
Goderich Mine [Member]    
Loss Contingencies [Line Items]    
Claims asserted against the Company 13  
Cash payment to settle 4.2  
Gain on payment to settle $ 0.7