Annual report pursuant to Section 13 and 15(d)

Stock Options - Stock options activity table - Key Employees (Details)

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Stock Options - Stock options activity table - Key Employees (Details) (USD $)
 3 Months Ended 12 Months Ended
Jul. 31, 2009
Apr. 30, 2013
Apr. 30, 2013
Stock Options
Key Employees
Apr. 30, 2012
Stock Options
Key Employees
Apr. 30, 2011
Stock Options
Key Employees
Shares          
Beginning Balance (in shares)   290,983 252,983 260,867 271,133
Granted (in shares) 8,333 41,667 41,667 48,000 23,167
Exercised (in shares)            (1,667)
Expired (in shares)   (21,075) (14,408) (55,884) (31,766)
Ending balance (in shares)   311,575 280,242 252,983 260,867
Exercise price per share          
Beginning balance (in dollars per share) lower range     $ 6.36 $ 7.68 $ 7.68
Beginning balance (in dollars per share) upper range     $ 24.54 $ 47.88 $ 145.50
Granted (in dollars per share) lower range     $ 4.14 $ 6.36 $ 9.48
Granted (in dollars per share) upper range     $ 4.14 $ 6.72 $ 12.96
Exercised (in dollars per share) lower range           $ 7.68
Exercised (in dollars per share) upper range           $ 7.68
Expired (in dollars per share) lower range     $ 6.72 $ 6.72 $ 9.48
Expired (in dollars per share) upper range     $ 24.54 $ 47.88 $ 145.50
Ending balance (in dollars per share) lower range     $ 2.44 $ 6.36 $ 7.68
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 $ 13.70 $ 16.72 $ 19.15
Granted (in dollars per share)   $ 3.12 $ 4.14 $ 6.59 $ 10.55
Exercised (in dollars per share)            $ 7.68
Expired (in dollars per share)     $ 15.49 $ 21.67 $ 33.40
Ending balance (in dollars per share)   $ 12.40 $ 12.04 $ 13.70 $ 16.72