Goodwill Balance by Reportable Segments and Reporting Unit (Detail) $ in Thousands	Apr. 30, 2018 USD ($)
Goodwill
Goodwill, beginning balance	$ 2,344
Goodwill, ending balance	2,344
Medical Imaging | Medical Imaging Reporting Unit
Goodwill
Goodwill, beginning balance	1,800
Goodwill, ending balance	1,800
Security and Detection | Security And Detection Reporting Unit
Goodwill
Goodwill, beginning balance	500
Goodwill, ending balance	$ 500