Reportable Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017	Jul. 31, 2017
Product revenue:
Product revenue	$ 117,156	$ 120,791	$ 349,599	$ 371,373
Engineering revenue:
Engineering revenue	2,815	1,371	6,419	3,448
Net revenue:
Total net revenue	119,971	122,162	356,018	374,821
Income (loss) from operations:
Total (loss) income from operations	7,311	(64,603)	30,928	(51,195)
Total other income (loss), net	328	57	1,504	(357)
Income before income taxes	7,639	(64,546)	32,432	(51,552)
Identifiable total assets by segment:
Assets	580,069		580,069		$ 538,083
Total Identifiable Assets
Identifiable total assets by segment:
Assets	577,700		577,700		535,700
Reportable segments
Identifiable total assets by segment:
Assets	342,100		342,100		338,700
Corporate
Identifiable total assets by segment:
Identifiable assets (excluding goodwill)	235,600		235,600		197,000
Medical Imaging
Product revenue:
Product revenue	59,800	68,200	173,800	205,900
Engineering revenue:
Engineering revenue	1,600	1,300	4,000	3,100
Net revenue:
Total net revenue	61,400	69,500	177,800	209,000
Income (loss) from operations:
Total (loss) income from operations	5,400	12,200	17,600	31,300
Medical Imaging | Reportable segments
Identifiable total assets by segment:
Assets	161,600		161,600		169,100
Ultrasound
Product revenue:
Product revenue	42,000	34,800	122,700	110,700
Engineering revenue:
Engineering revenue	200		300	200
Net revenue:
Total net revenue	42,200	34,800	123,000	110,900
Income (loss) from operations:
Total (loss) income from operations		(79,300)	5,700	(89,700)
Ultrasound | Reportable segments
Identifiable total assets by segment:
Assets	136,600		136,600		133,600
Security and Detection
Product revenue:
Product revenue	15,400	17,800	53,100	54,800
Engineering revenue:
Engineering revenue	1,000	100	2,100	100
Net revenue:
Total net revenue	16,400	17,900	55,200	54,900
Income (loss) from operations:
Total (loss) income from operations	1,900	$ 2,500	7,600	$ 7,200
Security and Detection | Reportable segments
Identifiable total assets by segment:
Assets	$ 43,900		$ 43,900		$ 36,000