Revenue by geographic location (Details) (USD $)	3 Months Ended		6 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012
Revenues by geographic location	$ 7,410,229	$ 6,959,023	$ 14,776,959	$ 14,957,508
United States
Revenues by geographic location	6,132,297	6,005,147	12,315,098	11,980,351
Europe
Revenues by geographic location	658,421	628,238	1,529,048	1,950,160
Other (principally Asia Pacific Region)
Revenues by geographic location	$ 619,511	$ 325,638	$ 932,813	$ 1,026,997