Stock Repurchase Program - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2016	Nov. 30, 2015	Nov. 30, 2016	Nov. 30, 2015
Stock Repurchase Programs [Line Items]
Authorization of stock repurchase program			Jan. 08, 2008
Shares repurchased	0	100,000	0	400,000
Shares repurchased, value		$ 4.4		$ 17.2
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