Reportable Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2017	Apr. 30, 2016	Jul. 31, 2016
Product revenue:
Product revenue		$ 120,791	$ 126,376	$ 371,373	$ 366,443
Engineering revenue:
Engineering revenue		1,371	1,604	3,448	4,354
Net revenue:
Total net revenue		122,162	127,980	374,821	370,797
Income (loss) from operations:
Total (loss) income from operations		(64,603)	7,626	(51,195)	11,123
Total other income (loss), net		100	(900)	(400)	(4,900)
(Loss) income before income taxes		(64,546)	6,692	(51,552)	6,224
Identifiable total assets by segment:
Assets		567,677		567,677		$ 632,897
Total Identifiable Assets
Identifiable total assets by segment:
Assets		565,300		565,300		559,000
Reportable segments
Identifiable total assets by segment:
Assets		372,200		372,200		393,400
Corporate
Identifiable total assets by segment:
Identifiable assets (excluding goodwill)	[1]	193,100		193,100		165,600
Medical Imaging
Product revenue:
Product revenue		68,200	71,900	205,900	208,700
Engineering revenue:
Engineering revenue		1,300	900	3,100	2,600
Net revenue:
Total net revenue		69,500	72,900	209,000	211,300
Income (loss) from operations:
Total (loss) income from operations		12,200	10,200	31,300	28,200
Medical Imaging | Reportable segments
Identifiable total assets by segment:
Assets		182,800		182,800		191,100
Ultrasound
Product revenue:
Product revenue		34,800	36,800	110,700	115,900
Engineering revenue:
Engineering revenue			800	200	1,700
Net revenue:
Total net revenue		34,800	37,600	110,900	117,600
Income (loss) from operations:
Total (loss) income from operations		(79,300)	(5,000)	(89,700)	(19,500)
Ultrasound | Reportable segments
Identifiable total assets by segment:
Assets		146,800		146,800		152,500
Security and Detection
Product revenue:
Product revenue		17,800	17,600	54,800	41,800
Engineering revenue:
Engineering revenue		100	(100)	100	100
Net revenue:
Total net revenue		17,900	17,500	54,900	41,900
Income (loss) from operations:
Total (loss) income from operations		2,500	$ 2,400	7,200	$ 2,400
Security and Detection | Reportable segments
Identifiable total assets by segment:
Assets		$ 42,600		$ 42,600		$ 49,800

[1] Includes cash and cash equivalents of $144.9 million and $97.3 million as of April 30, 2017 and July 31, 2016, respectively.