Debt And Receivables Securitization (Details) (USD $)	6 Months Ended
	Nov. 30, 2011
Debt And Receivables Securitization [Line Items]
Maximum borrowing capacity	$ 400,000,000
Maturity date	May 2013
Borrowings outstanding	136,050,000
Remaining borrowing capacity	255,000,000
Applicable variable rate	0.90%
Credit facility interest rate terms	At November 30, 2011, the applicable variable rate, based on LIBOR, was 0.9%.
WNCL [Member]
Debt And Receivables Securitization [Line Items]
Maximum borrowing capacity	9,500,000
Maturity date	November 2012
Borrowings outstanding	5,036,000
Applicable variable rate	2.50%
Credit facility interest rate terms	The applicable variable rate at November 30, 2011 was 2.5%.
Financial Stand-By Letters Of Credit [Member]
Debt And Receivables Securitization [Line Items]
Outstanding stand-by letters of credit amount for third-party beneficiaries	8,950,000
Accounts Receivable Securitization Facility [Member]
Debt And Receivables Securitization [Line Items]
Number of days past due trade accounts receivables are ineligible for securitization	90
Maximum borrowing capacity	100,000,000
Maturity date	January 2012
Borrowings outstanding	$ 85,000,000