Employee Exposure Standards by Regulatory Agencies (Detail)	12 Months Ended
	May 31, 2012
Occupational Safety And Health Administration
Loss Contingencies [Line Items]
Employee exposure standards, nanograms per cubic meter	5,000
National Institute For Occupational Safety And Health
Loss Contingencies [Line Items]
Employee exposure standards, nanograms per cubic meter	1,000
California Environmental Protection Agency
Loss Contingencies [Line Items]
Employee exposure standards, nanograms per cubic meter	200