Rollforward of Accumulated Goodwill Impairment Losses by Reportable Segment and Reporting Unit (Detail) $ in Millions	Apr. 30, 2018 USD ($)
Finite Lived Intangible Assets [Line Items]
Accumulated impairment losses, beginning balance	$ (71.6)
Accumulated impairment losses, ending balance	(71.6)
Ultrasound | Ultrasound Reporting Unit
Finite Lived Intangible Assets [Line Items]
Accumulated impairment losses, beginning balance	(55.2)
Accumulated impairment losses, ending balance	(55.2)
Ultrasound | Oncura Reporting Unit
Finite Lived Intangible Assets [Line Items]
Accumulated impairment losses, beginning balance	(16.4)
Accumulated impairment losses, ending balance	$ (16.4)