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