Goderich Tornado (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended	38 Months Ended
	Sep. 30, 2014	Dec. 31, 2014	Sep. 30, 2014
Goderich Tornado [Abstract]
Total insurance advances			$ 114.9
Deferred revenue		$ 28.6
Total insurance advances received and recorded as reduction to salt product costs			26.9
Insurance proceeds for replacement of property, plant and equipment and business interruption			83.3
Deferred released in connection with settlement	$ 83.3		$ 83.3
Gain recorded as reduction to production cost	82.3
Gain recorded as reduction to selling, general and administrative expenses	$ 1.0