Summary of Property, Plant and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2013	May 31, 2012
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 174,839	$ 152,675
Accumulated depreciation and amortization	(102,336)	(90,634)
Property, plant and equipment, net	72,503	62,041
Land
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,112	1,285
Buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	18,017	15,095
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	133,738	121,533
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,668	2,246
Computers and computer software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	8,600	7,980
Automobiles
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,856	2,624
Construction in progress
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 4,848	$ 1,912