Legal Proceedings and Contingent Liabilities - Additional Information (Details)	12 Months Ended		2 Months Ended	12 Months Ended
	May 31, 2013 sample	May 31, 2008 case	Apr. 09, 2008 Crestmore Plant	May 31, 2013 Crestmore Plant Plaintiff defendant	May 31, 2013 Oro Grande Plant Plaintiff	May 31, 2013 Shellman Lawsuit LegalMatter	May 31, 2013 Maximum Crestmore Plant	May 31, 2013 Maximum Oro Grande Plant	May 31, 2013 Assuming Continuous Exposure For Seventy Years Minimum Crestmore Plant Person	May 31, 2013 Assuming Continuous Exposure For Seventy Years Maximum Crestmore Plant Person
Loss Contingencies [Line Items]
Average level of hexavalent chromium, nanograms per cubic meter			2.43				1.0	1.0
Increase in risk of cancer, instances per million people									250	500
SCAQMD calculation of cancer risk, time frame assumption				70 years
Number of excess cancer cases found by researcher for the period 1996-2005		0
Number of subsidiary defendants in class action lawsuit				3
Number of additional class action lawsuits filed						5
Number of lawsuits stayed						4
Number of individual plaintiffs involved in lawsuit				3,000	300
Number of plaintiffs remaining				2,000	250
Number of samples to date containing chrome 6 levels above 1.0 ng/m3	0