Reportable Segment Information (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Jul. 31, 2016	Jul. 31, 2015
Segment Reporting Information [Line Items]
Restructuring charge	$ 267	$ 3,147	$ 299	$ 6,430
Asset impairment charges	10,423		10,423
Cash and cash equivalents	152,990	120,067	152,990	120,067	$ 118,697	$ 123,800
Medical Imaging
Segment Reporting Information [Line Items]
Restructuring charge	90	1,900	110	4,000
Ultrasound
Segment Reporting Information [Line Items]
Restructuring charge	170	600	180	1,300
Security and Detection
Segment Reporting Information [Line Items]
Restructuring charge	10	600	10	1,200
Oncura
Segment Reporting Information [Line Items]
Contingent consideration charges	(8,200)		(8,100)
Asset impairment charges	9,800	$ 10,100	9,800	$ 10,100
Corporate
Segment Reporting Information [Line Items]
Cash and cash equivalents	$ 139,900		$ 139,900		$ 97,300