Property and Equipment - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Jul. 31, 2012	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Property, Plant and Equipment [Line Items]
Depreciation expense		$ 2,600,000	$ 3,300,000	$ 6,100,000
Asset impairment charge	790,000	790,000		1,076,000
Asset impairment charge				$ 1,100,000
Tyngsborough Massachusetts [Member]
Property, Plant and Equipment [Line Items]
Ownership of land		102