Revenue by geographic location (Details) (USD $)	3 Months Ended		9 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
Revenues by geographic location	$ 6,438,961	$ 8,420,135	$ 21,396,469	$ 29,095,949
United States
Revenues by geographic location	4,572,914	6,091,393	16,553,265	23,357,207
Europe
Revenues by geographic location	1,217,323	1,463,481	3,167,483	3,886,481
Other (principally Asia Pacific Region)
Revenues by geographic location	$ 648,724	$ 865,261	$ 1,675,721	$ 1,852,261