Intangible Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 3.4	$ 2.6	$ 1.0
Amortization expense, 2014	3.6
Amortization expense, 2015	3.6
Amortization expense, 2016	3.6
Amortization expense, 2017	3.6
Amortization expense, 2018	$ 3.6