Intangible Assets and Goodwill - Additional Information (Detail)			3 Months Ended		12 Months Ended
	Dec. 31, 2016 USD ($)	Jan. 08, 2016 USD ($)	Apr. 30, 2017 USD ($)	Jan. 31, 2017 USD ($)	Jul. 31, 2017 USD ($) Segment Unit	Jul. 31, 2016 USD ($)	Jul. 31, 2015 USD ($)
Goodwill and Intangible Assets Disclosure [Line Items]
Amortization expense related to acquired finite-lived intangible assets					$ 7,400,000	$ 8,400,000	$ 8,900,000
Carrying value of intangible assets					18,300,000	37,600,000
Goodwill					2,344,000	73,915,000
Goodwill expected to be deductible for tax purposes					$ 10,500,000	10,500,000
Number of Reporting Units | Unit					4
Number Of Reportable Segments | Segment					3
Impairment of goodwill					$ 71,600,000
Adjustments in contingent consideration					(10,239,000)	141,000	$ (62,000)
Intangible assets					25,925,000	45,194,000
Customer relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets					15,000,000	21,900,000
Trade names
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets						900,000
Developed technologies
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets					3,300,000	14,800,000
Ultrasound
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill	$ 55,200,000		$ 0
Impairment of goodwill	$ 0		55,200,000
Percentage of goodwill excess fair value over carrying value	25.00%
Intangible assets					8,600,000
Security and Detection
Goodwill and Intangible Assets Disclosure [Line Items]
Impairment of goodwill	$ 0
Medical Imaging
Goodwill and Intangible Assets Disclosure [Line Items]
Impairment of goodwill	$ 0
Oncura
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		$ 16,400,000	0
Impairment of goodwill			6,600,000	$ 9,800,000
Adjustments in contingent consideration					(10,200,000)	100,000
Fair value of contingent consideration obligation		$ 10,100,000	0		0	10,200,000
Oncura | General and Administrative
Goodwill and Intangible Assets Disclosure [Line Items]
Adjustments in contingent consideration			10,200,000
Oncura | Customer relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets, estimated useful lives		6 years
Oncura | Trade names
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets, estimated useful lives		5 years
Oncura | Ultrasound
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets					3,200,000
Intangible assets impairment charge			3,200,000
Adjustments in contingent consideration					(10,200,000)
Oncura | Ultrasound | Customer relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets impairment charge			2,400,000		2,400,000
Oncura | Ultrasound | Trade names
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets impairment charge			800,000		800,000
PocketSonics
Goodwill and Intangible Assets Disclosure [Line Items]
Adjustments in contingent consideration			0		0
PocketSonics | Ultrasound
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets			8,100,000
PocketSonics | Ultrasound | Technology
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets impairment charge			$ 8,100,000		8,100,000
Pathfinder Therapeutics Inc | Security and Detection
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets				600,000
Intangible assets impairment charge				600,000
Pathfinder Therapeutics Inc | Security and Detection | Trade names
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets impairment charge				100,000	100,000
Pathfinder Therapeutics Inc | Security and Detection | Developed technologies
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets impairment charge				$ 500,000	500,000
Trade names
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite lived intangible assets					$ 7,600,000	$ 7,600,000
Minimum
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets, estimated useful lives					1 year
Maximum
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets, estimated useful lives					14 years