Basis of Presentation - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2013	Feb. 29, 2012	Feb. 28, 2013	Feb. 29, 2012	May 31, 2012
Basis of Presentation [Line Items]
Shipping and handling cost	$ 780	$ 924	$ 2,735	$ 3,096
Assets, liabilities, revenues and expenses of foreign subsidiaries			Less than 10% of consolidated amounts
Demonstration equipment	6,005		6,005		5,495
Reduction in selling, general and administrative expenses		$ 2,680		$ 8,233
Minimum
Basis of Presentation [Line Items]
Operating lease agreements Period			1 year
Finance lease agreements Period			1 year
Maximum
Basis of Presentation [Line Items]
Operating lease agreements Period			3 years
Finance lease agreements Period			3 years
Period for demonstration equipment included in other assets			2 years