Summary of Property, Plant and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2013	May 31, 2013
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 185,682	$ 179,990
Accumulated depreciation and amortization	(108,958)	(105,051)
Property, plant, and equipment, net	76,724	74,939
Land
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,092	3,108
Buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	20,603	18,445
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	141,102	137,439
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,668	4,469
Computers and computer software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	9,146	8,871
Automobiles
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,572	3,842
Construction in progress
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 3,499	$ 3,816