Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Stock-Based Compensation - Fair Value of Each Stock Option Granted (Details)

v2.4.0.8
Summary of Significant Accounting Policies - Stock-Based Compensation - Fair Value of Each Stock Option Granted (Details) (Stock Option Plan)
12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Stock Option Plan
     
Expected life (years) 3.0 to 5.75 3.0 to 3.3 3.0 to 6.0
Expected volatility 77.00% 77.00%  
Expected volatility minimum     56.00%
Expected volatility maximum     79.00%
Expected dividend yield         
Expected forfeiture rate 5.00% 5.00% 5.00%
Risk-free interest rate minimum 0.50% 0.50% 0.70%
Risk-free interest rate maximum 0.60% 0.60% 2.90%