Annual report pursuant to Section 13 and 15(d)

Stock Options - Stock options activity table - Non employees (Details)

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Stock Options - Stock options activity table - Non employees (Details) (USD $)
 3 Months Ended 12 Months Ended
Jul. 31, 2009
Apr. 30, 2013
Apr. 30, 2013
Stock Options
Non Employees Directors
Apr. 30, 2012
Stock Options
Non Employees Directors
Apr. 30, 2011
Stock Options
Non Employees Directors
Shares          
Beginning Balance (in shares)   290,983 38,000 47,333 53,333
Granted (in shares) 8,333 41,667         
Exercised (in shares)              
Expired (in shares)   (21,075) (6,667) (9,333) (6,000)
Ending balance (in shares)   311,575 31,333 38,000 47,333
Exercise price per share          
Beginning balance (in dollars per share) lower range     $ 11.94 $ 11.94 $ 11.94
Beginning balance (in dollars per share) upper range     $ 24.54 $ 47.88 $ 47.88
Granted (in dollars per share) lower range             
Granted (in dollars per share) upper range             
Exercised (in dollars per share) lower range             
Exercised (in dollars per share) upper range             
Expired (in dollars per share) lower range     $ 17.94 $ 28.20 $ 38.52
Expired (in dollars per share) upper range     $ 19.98 $ 47.88 $ 39.78
Ending balance (in dollars per share) lower range     $ 11.94 $ 11.94 $ 11.94
Ending balance (in dollars per share) upper range     $ 24.54 $ 24.54 $ 47.88
Weighted average exercise price per share          
Beginning balance (in dollars per share)   $ 14.04 $ 16.23 $ 20.25 $ 22.40
Granted (in dollars per share)   $ 3.12         
Exercised (in dollars per share)              
Expired (in dollars per share)     $ 19.16 $ 36.64 $ 39.36
Ending balance (in dollars per share)   $ 12.40 $ 15.60 $ 16.23 $ 20.25