Summary of Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified			6 Months Ended
	Jan. 31, 2013	Jul. 31, 2012	Jan. 31, 2013 Minimum	Jan. 31, 2013 Maximum	Jan. 31, 2013 Equipment spares Minimum	Jan. 31, 2013 Equipment spares Maximum	Jan. 31, 2013 Machinery, equipment and internally manufactured systems Minimum	Jan. 31, 2013 Machinery, equipment and internally manufactured systems Maximum	Jan. 31, 2013 Furniture and Fixtures Minimum	Jan. 31, 2013 Furniture and Fixtures Maximum	Jan. 31, 2013 Purchased Software	Jan. 31, 2013 Leasehold Improvements	Jan. 31, 2013 Leasehold Improvements Maximum
Property, Plant and Equipment [Line Items]
Equipment spares	$ 51,036	$ 57,841
Machinery, equipment and internally manufactured systems	39,078	38,067
Office furniture and equipment	3,664	3,885
Purchased software	2,867	2,870
Land	2,524	2,524
Leasehold improvements	6,235	6,187
Property and equipment, gross	105,404	111,374
Less: accumulated depreciation and amortization	(87,660)	(93,145)
Property and equipment, net	$ 17,744	$ 18,229
Property plant and equipment useful life			3 years	7 years	5 years	7 years	3 years	7 years	3 years	7 years	3 years		10 years
Property plant and equipment useful life												Term of lease or useful life, not to exceed 10 years