Intangible Assets and Goodwill - Additional Information (Detail)		3 Months Ended			9 Months Ended
	Dec. 31, 2016 USD ($)	Apr. 30, 2017 USD ($)	Jan. 31, 2017 USD ($)	Apr. 30, 2016 USD ($)	Apr. 30, 2017 USD ($) Unit Segment	Apr. 30, 2016 USD ($)	Jul. 31, 2016 USD ($)
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite lived intangible assets		$ 7,600,000			$ 7,600,000		$ 7,600,000
Amortization expense related to acquired intangible assets		1,900,000		$ 2,300,000	5,900,000	$ 6,300,000
Carrying value of intangible assets		19,800,000			19,800,000		37,600,000
Intangible assets impairment charge					11,900,000
Goodwill		2,344,000			$ 2,344,000		73,915,000
Number of Reporting Units | Unit					4
Number of Reportable Segments | Segment					3
Impairment of goodwill					$ 71,600,000
Intangible assets		27,406,000			27,406,000		45,194,000
Gain from adjustment of contingent consideration liability					(10,238,000)
Customer relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets		16,000,000			16,000,000		21,900,000
Trade names
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets							900,000
Ultrasound
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill	$ 55,100,000	0			0		71,600,000
Impairment of goodwill	$ 0	55,100,000			71,600,000
Percentage of goodwill excess fair value over carrying value	25.00%
Intangible assets		9,300,000			9,300,000
Security and Detection
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		500,000			500,000		500,000
Impairment of goodwill	$ 0
Medical Imaging
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		1,800,000			1,800,000		$ 1,800,000
Impairment of goodwill	$ 0
Oncura
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		0			0
Impairment of goodwill		6,700,000	$ 9,800,000
Fair value of contingent consideration obligation		0			0
Oncura | General and Administrative
Goodwill and Intangible Assets Disclosure [Line Items]
Gain from adjustment of contingent consideration liability		2,100,000			10,200,000
Oncura
Goodwill and Intangible Assets Disclosure [Line Items]
Gain from adjustment of contingent consideration liability		(2,100,000)			(10,200,000)
Fair value of contingent consideration obligation		0			0
Oncura | Ultrasound
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets		3,100,000			3,100,000
Intangible assets impairment charge		3,100,000
Oncura | Ultrasound | Customer relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets impairment charge		2,400,000
Oncura | Ultrasound | Trade names
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets impairment charge		700,000
PocketSonics
Goodwill and Intangible Assets Disclosure [Line Items]
Gain from adjustment of contingent consideration liability		0			0
PocketSonics | Ultrasound
Goodwill and Intangible Assets Disclosure [Line Items]
Carrying value of intangible assets		8,100,000			$ 8,100,000
Intangible assets impairment charge		8,100,000
PocketSonics | Ultrasound | Technology
Goodwill and Intangible Assets Disclosure [Line Items]
Intangible assets impairment charge		$ 8,100,000
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