Share-Based Awards and Options (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2011	Nov. 30, 2010	Nov. 30, 2011	Nov. 30, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share based employee compensation plans	4		4
Share-based compensation cost	$ 4,400,000	$ 4,200,000	$ 8,425,000	$ 7,690,000
Income tax benefit	$ 1,500,000	$ 1,500,000	$ 2,800,000	$ 2,700,000
2011 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance units	2		2
Shares available for future grant (in shares)	7.0		7.0
PRSU [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Earnable percentage of target shares of company stock			0.00%
PRSU [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Earnable percentage of target shares of company stock			200.00%
TSR [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period			3 years
TSR [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Earnable percentage of target shares of company stock			0.00%
TSR [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Earnable percentage of target shares of company stock			200.00%