$205 Million Convertible Note Offering - Additional Information (Detail) (USD $)	9 Months Ended
	Feb. 28, 2014	Feb. 28, 2013
Debt Instrument [Line Items]
Proceeds from not issuance, net	$ 262,211,000	$ 318,994,000
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 at a fixed rate of 2.25% on the Convertible Notes semi-annually in arrears on June 15thand December 15thof each year, beginning on June 15, 2014
Proceeds from not issuance, net	200,100,000
Straight debt rate	3.92%
Debt instrument, conversion rate	18.8905
Convertible notes, initial conversion price per share	$ 52.94
Unamortized debt discount	20,100,000
Notes redemption date	Dec. 20, 2017
Number of trading days	30 days
Principal amount of the notes to be repurchased, plus accrued and unpaid interest	100.00%
Convertible Notes | Minimum
Debt Instrument [Line Items]
Percentage of sales price of common stock exceeding conversion price	125.00%
Number of trading days for which a conversion price is in effect during any 30 consecutive trading day period	20 days
Convertible Notes | Liability Component
Debt Instrument [Line Items]
Issuance of note	184,300,000
Convertible Notes | Equity Component
Debt Instrument [Line Items]
Issuance of note	20,700,000
Unsecured Senior Notes 6.25% December 15, 2013
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%