Summary of Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified			3 Months Ended
	Oct. 31, 2013	Jul. 31, 2013	Oct. 31, 2013 Minimum	Oct. 31, 2013 Maximum	Oct. 31, 2013 Equipment spares Minimum	Oct. 31, 2013 Equipment spares Maximum	Oct. 31, 2013 Machinery, equipment and internally manufactured systems Minimum	Oct. 31, 2013 Machinery, equipment and internally manufactured systems Maximum	Oct. 31, 2013 Office furniture and equipment Minimum	Oct. 31, 2013 Office furniture and equipment Maximum	Oct. 31, 2013 Purchased software	Oct. 31, 2013 Leasehold improvements	Oct. 31, 2013 Leasehold improvements Maximum
Property, Plant and Equipment [Line Items]
Equipment spares	$ 58,110	$ 58,461
Machinery, equipment and internally manufactured systems	36,068	34,587
Office furniture and equipment	2,063	2,014
Purchased software	488	488
Land	2,524	2,524
Leasehold improvements	6,952	6,983
Property and equipment, gross	106,205	105,057
Less: accumulated depreciation and amortization	(89,227)	(88,410)
Property and equipment, net	$ 16,978	$ 16,647
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