Stock Repurchase Program - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2015	Feb. 28, 2014	Feb. 28, 2015	Feb. 28, 2014
Stock Repurchase Programs [Line Items]
Authorization of stock repurchase program			Jan. 08, 2008
Shares repurchased	550,000
Shares repurchased, value	$ 25,800	$ 28	$ 27,588	$ 6,895
Minimum
Stock Repurchase Programs [Line Items]
Shares authorized to be repurchased, per year	1,000,000		1,000,000
Maximum
Stock Repurchase Programs [Line Items]
Shares authorized to be repurchased, per year	2,000,000		2,000,000