Share-based Awards and Options - Employee Stock Purchase Plan (Details) (USD $)	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]
Share-based compensation expense	$ 5,300,000	$ 5,000,000	$ 17,300,000	$ 14,100,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized (in shares)	2,400,000		2,400,000
Maximum employee subscription amount			25,000
Maximum employee subscription rate	20.00%		20.00%
Discounted market value			85.00%
Shares issued in period, net (in shares)			1,100,000
Shares reserved for future issuance (in shares)	1,300,000		1,300,000
Share-based compensation expense	$ 100,000	$ 200,000	$ 400,000	$ 400,000
Weighted average grant-date fair value (in dollars per share)	$ 7	$ 6	$ 7	$ 6
Discount from market price			15.00%