$205 Million Convertible Note Offering - Additional Information (Detail) (USD $)	6 Months Ended
	Nov. 30, 2013	Nov. 30, 2012
Debt Instrument [Line Items]
Proceeds from not issuance, net	$ 2,776,000	$ 334,247,000
Unsecured Senior Notes
Debt Instrument [Line Items]
Interest rate on notes issue	6.70%
Notes maturity date	Nov. 01, 2015
Subsequent Event | Convertible Notes
Debt Instrument [Line Items]
Issuance of note	205,000,000
Interest rate on notes issue	2.25%
Notes maturity date	Dec. 15, 2020
Note Interest payment frequency, term	Interest on the Convertible Notes semi-annually on June 15th and December 15th of each year, beginning on June 15th, 2014
Debt instrument, conversion rate	18.8905
Principal amount of each convertible note	1,000
Convertible notes, initial conversion price per share	$ 52.94
Proceeds from not issuance, net	200,100,000
Subsequent Event | Unsecured Senior Notes
Debt Instrument [Line Items]
Notes maturity date	Dec. 15, 2013
Principal amount of unsecured senior notes, repayments	$ 200,000,000
Unsecured senior notes , interest rate	6.25%