Financial Information by Geographic Location (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues by geographic location	$ 6,603,463	$ 8,050,557	$ 19,991,917	$ 22,655,310
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues by geographic location	5,039,000	6,914,000	16,260,000	19,243,000
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues by geographic location	1,396,000	1,018,000	3,391,000	3,016,000
Other (principally Asia Pacific Region)
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues by geographic location	$ 168,000	$ 119,000	$ 341,000	$ 396,000