Debt (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended			12 Months Ended			12 Months Ended	3 Months Ended
	May 31, 2008	Aug. 31, 2012	May 31, 2003	May 31, 2008 Term Loan [Member]	Aug. 31, 2012 Unsecured Debt [Member]	Aug. 31, 2012 Secured Debt [Member]	May 31, 2008 Revolving Loan [Member]	Aug. 31, 2012 Federal Funds Rate [Member]	Aug. 31, 2012 Eurodollar Rate [Member]	Aug. 31, 2012 LIBOR Rate [Member]	Aug. 31, 2012 Notes Payable, Other Payables [Member]	Aug. 31, 2012 Standby Letter Of Credit [Member]	Aug. 31, 2012 Loan Agreement [Member]
Credit Facility Sanctioned During Period	$ 525.0						$ 325.0
Credit Facility Sanctioned				200.0
Additional Credit Facility Sanctioned							150.0
Line of Credit Facility, Interest Rate During Period								0.50%
Line of Credit Facility, Interest Rate Description									Eurodollar Rate for a one month interest period plus 1% plus an applicable spread ranging from 0.18% to 0.60%	London interbank offered rate (LIBOR) plus an applicable spread ranging from 1.18% to 1.60%
Line Of Credit Facility Base Rate Advances		0.18%
Line Of Credit Facility Eurodollar Rate Advances									1.18%
Line of Credit Facility, Commitment Fee Percentage Range Minimum		0.20%
Line of Credit Facility Fee Percentage Range Maximum		0.40%
Line Of Credit Facility Fee Percentage		0.20%
Line of Credit Facility, Amount Outstanding												6.6	1.4
Line of Credit, Current					20.0	33.8
Notes Payable, Noncurrent, Value			$ 175.0
Debt Instrument, Interest Rate, Stated Percentage											5.00%