Percentage of Net Product and Engineering Revenue from Major Customers (Parenthetical) (Detail) - Sales Revenue, Net - Largest customers	3 Months Ended		9 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2017	Apr. 30, 2016
Concentration Risk [Line Items]
Percentage of net product and engineering revenue	61.00%	62.00%	63.00%	62.00%
L-3
Concentration Risk [Line Items]
Percentage of net product and engineering revenue	11.00%	10.00%	10.00%
L-3 | Maximum
Concentration Risk [Line Items]
Percentage of net product and engineering revenue				10.00%
Toshiba
Concentration Risk [Line Items]
Percentage of net product and engineering revenue				11.00%
Toshiba | Maximum
Concentration Risk [Line Items]
Percentage of net product and engineering revenue		10.00%