Goderich Tornado (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 32 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Mar. 31, 2014
Dec. 31, 2013
Goderich Tornado [Abstract]        
Total insurance advances $ 13.7 $ 7.5 $ 100.0  
Total insurance advances received and recorded as reduction to salt product costs   0.8    
Deferred revenue 13.7 6.7    
Total amount recorded in deferred revenue since the tornado $ 68.0   $ 68.0 $ 56.5