Warranty - Reconciliation of Accrued Warranty and Related Expenses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Aug. 31, 2014	Aug. 31, 2013	May 31, 2014
Guarantees [Abstract]
Balance at the beginning of the period	$ 5,697	$ 5,882
Accruals for warranties	1,695	1,298
Settlements made during the period	(1,731)	(1,181)
Balance at the end of the period	5,661	5,999
Non-current balance included in other deferred liabilities	2,000	2,200	2,000
Accrued warranty and related expenses	$ 3,661	$ 3,799	$ 3,697