Changes in the Carrying of Goodwill by Reportable Segment and Reporting Unit (Detail) - USD ($)		3 Months Ended	12 Months Ended
	Dec. 31, 2016	Apr. 30, 2017	Jul. 31, 2017
Goodwill
Goodwill, beginning balance			$ 73,915,000
Impairment losses			(71,600,000)
Goodwill, ending balance			2,344,000
Medical Imaging
Goodwill
Impairment losses	$ 0
Medical Imaging | Medical Imaging Reporting Unit
Goodwill
Goodwill, beginning balance			1,800,000
Goodwill, ending balance			1,800,000
Ultrasound
Goodwill
Impairment losses	0	$ (55,200,000)
Goodwill, ending balance	55,200,000	$ 0
Ultrasound | Ultrasound Reporting Unit
Goodwill
Goodwill, beginning balance			55,200,000
Impairment losses			(55,200,000)
Ultrasound | Oncura Reporting Unit
Goodwill
Goodwill, beginning balance			16,400,000
Impairment losses			(16,400,000)
Security and Detection
Goodwill
Impairment losses	$ 0
Security and Detection | Security And Detection Reporting Unit
Goodwill
Goodwill, beginning balance			500,000
Goodwill, ending balance			$ 500,000