Legal Proceedings And Contingent Liabilities - Additional Information (Detail)	2 Months Ended	12 Months Ended
	Apr. 09, 2008	May 31, 2012 LegalMatter
Loss Contingencies [Line Items]
Average level of hexavalent chromium, nanograms per cubic meter	2.43	1.00
SCAQMD calculation of cancer risk, time frame assumption, in years		70
Number of subsidiary defendants in class action lawsuit		3
Crestmore Plant
Loss Contingencies [Line Items]
Number of individual plaintiffs involved in lawsuit		3,000
Number of Plaintiffs remaining		2,000
Oro Grande Plant
Loss Contingencies [Line Items]
Number of individual plaintiffs involved in lawsuit		300
Number of Plaintiffs remaining		250
Shellman Lawsuit
Loss Contingencies [Line Items]
Number of additional class action lawsuits filed		5
Number of lawsuits stayed		4
Assuming Continuous Exposure For Seventy Years | Minimum
Loss Contingencies [Line Items]
Increase in risk of cancer, instances per million people		250
Assuming Continuous Exposure For Seventy Years | Maximum
Loss Contingencies [Line Items]
Increase in risk of cancer, instances per million people		500