Revenue by geographic location (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012 United States	Oct. 31, 2011 United States	Oct. 31, 2012 United States	Oct. 31, 2011 United States	Oct. 31, 2012 Europe	Oct. 30, 2011 Europe	Oct. 31, 2012 Europe	Oct. 31, 2011 Europe	Oct. 31, 2012 Other (principally Asia Pacific Region)	Oct. 31, 2011 Other (principally Asia Pacific Region)	Oct. 31, 2012 Other (principally Asia Pacific Region)	Oct. 31, 2011 Other (principally Asia Pacific Region)
Revenues by geographic location	$ 6,959,023	$ 10,406,008	$ 14,957,508	$ 20,675,814	$ 6,005,147	$ 8,570,416	$ 11,980,351	$ 17,264,993	$ 628,238	$ 1,224,412	$ 1,950,160	$ 2,423,706	$ 325,638	$ 611,180	$ 1,026,997	$ 987,115