Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jan. 31, 2018	Jul. 31, 2017
Property, Plant and Equipment [Line Items]
Equipment spares	$ 27,792	$ 27,680
Machinery, equipment and internally manufactured systems	33,678	30,707
Office furniture and equipment	1,558	1,302
Purchased software	555	547
Land	2,508	2,508
Buildings	7,990	7,990
Leasehold improvements	9,969	9,679
Property and equipment, gross	84,050	80,413
Accumulated depreciation and amortization	(53,959)	(51,904)
Property and equipment, net	$ 30,091	$ 28,509
Property plant and equipment estimated useful life	7 years	7 years
Equipment spares
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful life	7 years
Machinery, equipment and internally manufactured systems | Minimum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful life	3 years
Machinery, equipment and internally manufactured systems | Maximum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful life	7 years
Office furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful life	3 years
Office furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful life	7 years
Purchased software
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful life	3 years
Building | Minimum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful life	10 years
Building | Maximum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful life	40 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	Term of lease or useful life, not to exceed 10 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property plant and equipment estimated useful life	10 years