Reportable Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Jul. 31, 2017
Product revenue:
Product revenue	$ 126,691	$ 130,330	$ 232,444	$ 250,582
Engineering revenue:
Engineering revenue	2,481	1,204	3,604	2,077
Net revenue:
Total net revenue	129,172	131,534	236,048	252,659
Income (loss) from operations:
Total (loss) income from operations	15,743	9,450	23,618	13,408
Total other income (loss), net	939	28	1,175	(414)
Income before income taxes	16,682	9,478	24,793	12,994
Identifiable total assets by segment:
Assets	562,112		562,112		$ 538,083
Total Identifiable Assets
Identifiable total assets by segment:
Assets	559,800		559,800		535,700
Reportable segments
Identifiable total assets by segment:
Assets	338,400		338,400		338,700
Corporate
Identifiable total assets by segment:
Identifiable assets (excluding goodwill)	221,400		221,400		197,000
Medical Imaging
Product revenue:
Product revenue	62,000	71,200	114,100	137,700
Engineering revenue:
Engineering revenue	1,400	1,200	2,400	1,900
Net revenue:
Total net revenue	63,400	72,400	116,500	139,600
Income (loss) from operations:
Total (loss) income from operations	7,400	12,200	12,200	18,900
Medical Imaging | Reportable segments
Identifiable total assets by segment:
Assets	161,800		161,800		169,100
Ultrasound
Product revenue:
Product revenue	43,400	40,300	80,700	75,900
Engineering revenue:
Engineering revenue	100		100	200
Net revenue:
Total net revenue	43,500	40,300	80,800	76,100
Income (loss) from operations:
Total (loss) income from operations	4,300	(4,500)	5,600	(10,300)
Ultrasound | Reportable segments
Identifiable total assets by segment:
Assets	134,900		134,900		133,600
Security and Detection
Product revenue:
Product revenue	21,300	18,800	37,600	37,000
Engineering revenue:
Engineering revenue	1,000		1,100
Net revenue:
Total net revenue	22,300	18,800	38,700	37,000
Income (loss) from operations:
Total (loss) income from operations	4,000	$ 1,800	5,800	$ 4,800
Security and Detection | Reportable segments
Identifiable total assets by segment:
Assets	$ 41,700		$ 41,700		$ 36,000