Stock-Based Compensation Plans - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2014	Feb. 28, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, expiration period			10 years
Options granted during period	0		0
Shares available for future awards	2,697,646		2,697,646
Closing market price of common stock			$ 84.9
Aggregate intrinsic value of stock options outstanding	$ 56.7		$ 56.7
Aggregate intrinsic value of exercisable stock options	37.2		37.2
Total intrinsic value of options exercised	5.8	5.3	6.6	6.3
Common stock reserved for the settlement of stock-based compensation	4,000,000		4,000,000
Liabilities increased (decreased) stock-based compensation		1.0	1.7
Tax expense recognized in statements of operations for stock-based compensation			0	0.1
Total unrecognized compensation cost related to stock options, restricted stock payments, and stock awards expected to be recognized	12.6		12.6
Unrecognized compensation cost related to stock options expected to be recognized, 2015			4.9
Unrecognized compensation cost related to stock options expected to be recognized, 2016			4.1
Unrecognized compensation cost related to stock options expected to be recognized, 2017			3.1
Unrecognized compensation cost related to stock options expected to be recognized, 2018			0.5
Selling, General and Administrative Expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation included in selling, general and administrative expense	1.4	2.7	5.4	7.0
Selling, General and Administrative Expenses | Company's Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation included in selling, general and administrative expense			$ 1.0
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			4 years
RSUs granted			85,219
RSU granted, average stock price on date of grant			$ 70.68
Market-Based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs granted			54,512
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, outstanding	133,315		133,315
Deferred Compensation Agreements To Be Settled In Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, outstanding	5,495		5,495