Reportable Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Product revenue:
Product revenue									$ 484,173	$ 502,752	$ 531,161
Engineering revenue:
Engineering revenue									2,199	6,096	9,130
Net revenue:
Total net revenue	$ 111,600	$ 122,200	$ 131,500	$ 121,100	$ 138,100	$ 128,000	$ 127,900	$ 114,900	486,372	508,848	540,291
Income (loss) from operations:
Total (loss) income from operations									(66,760)	25,213	40,599
Total other income (loss), net									500	(4,900)	400
(Loss) income before income taxes									(66,263)	20,316	41,033
Identifiable total assets by segment:
Assets	538,083				632,897				538,083	632,897
Share-based compensation expense:
Share-based compensation expense									9,430	8,864	10,938
Depreciation and amortization:
Depreciation and amortization									23,000	23,500	23,300
Total Identifiable Assets
Identifiable total assets by segment:
Assets	535,700				559,000				535,700	559,000
Reportable segments
Identifiable total assets by segment:
Assets	338,700				393,400				338,700	393,400
Corporate
Identifiable total assets by segment:
Identifiable assets (excluding goodwill)	197,000				165,600				197,000	165,600
Medical Imaging
Product revenue:
Product revenue									269,200	285,800	288,600
Engineering revenue:
Engineering revenue									5,000	3,400	4,000
Net revenue:
Total net revenue									274,200	289,200	292,600
Income (loss) from operations:
Total (loss) income from operations									38,000	38,600	37,900
Share-based compensation expense:
Share-based compensation expense									5,300	3,900	4,900
Depreciation and amortization:
Depreciation and amortization									10,800	11,300	11,100
Medical Imaging | Reportable segments
Identifiable total assets by segment:
Assets	169,100				191,100				169,100	191,100
Ultrasound
Product revenue:
Product revenue									148,000	160,800	163,600
Engineering revenue:
Engineering revenue									(1,100)	2,400	2,600
Net revenue:
Total net revenue									146,900	163,200	166,200
Income (loss) from operations:
Total (loss) income from operations									(108,000)	(18,800)	(7,900)
Share-based compensation expense:
Share-based compensation expense									2,500	2,600	3,200
Depreciation and amortization:
Depreciation and amortization									10,500	10,400	10,500
Ultrasound | Reportable segments
Identifiable total assets by segment:
Assets	133,600				152,500				133,600	152,500
Security and Detection
Product revenue:
Product revenue									67,000	56,100	79,000
Engineering revenue:
Engineering revenue									(1,700)	300	2,500
Net revenue:
Total net revenue									65,300	56,400	81,500
Income (loss) from operations:
Total (loss) income from operations									3,200	5,400	10,600
Share-based compensation expense:
Share-based compensation expense									1,600	2,300	2,800
Depreciation and amortization:
Depreciation and amortization									1,700	1,800	$ 1,700
Security and Detection | Reportable segments
Identifiable total assets by segment:
Assets	$ 36,000				$ 49,800				$ 36,000	$ 49,800