Subsequent Events - Additional Information (Detail) - USD ($)			12 Months Ended
	Jul. 16, 2015	Jun. 12, 2015	May. 31, 2015	May. 31, 2014	May. 31, 2013
Subsequent Event [Line Items]
Dividends declared per share			$ 0.80	$ 0.80	$ 1.80
Subsequent Event
Subsequent Event [Line Items]
Dividends declared per share		$ 0.125
Dividend payment date		Jul. 10, 2015
Dividend payment shareholders record date		Jun. 22, 2015
Chief Financial Officer | Subsequent Event
Subsequent Event [Line Items]
Severance costs	$ 251,825