Rollforward of Accumulated Goodwill Impairment Losses by Reportable Segment and Reporting Unit (Detail) - USD ($)		3 Months Ended	12 Months Ended
	Dec. 31, 2016	Apr. 30, 2017	Jul. 31, 2017
Finite Lived Intangible Assets [Line Items]
Impairment losses			$ (71,600,000)
Accumulated impairment losses, ending balance			(71,600,000)
Medical Imaging
Finite Lived Intangible Assets [Line Items]
Impairment losses	$ 0
Ultrasound
Finite Lived Intangible Assets [Line Items]
Impairment losses	0	$ (55,200,000)
Ultrasound | Ultrasound Reporting Unit
Finite Lived Intangible Assets [Line Items]
Impairment losses			(55,200,000)
Accumulated impairment losses, ending balance			(55,200,000)
Ultrasound | Oncura Reporting Unit
Finite Lived Intangible Assets [Line Items]
Impairment losses			(16,400,000)
Accumulated impairment losses, ending balance			$ (16,400,000)
Security and Detection
Finite Lived Intangible Assets [Line Items]
Impairment losses	$ 0