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Stockholders' Equity (Details Textual) (USD $)
 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
Apr. 30, 2012
Apr. 30, 2011
Oct. 31, 2012
General and Administrative Expense [Member]
Oct. 31, 2012
General and Administrative Expense [Member]
Oct. 31, 2011
General and Administrative Expense [Member]
Oct. 31, 2012
Former President and Chief Executive Officer [Member]
Oct. 31, 2012
PSUs [Member]
Oct. 31, 2011
PSUs [Member]
Oct. 31, 2012
PSUs [Member]
Executive Officer [Member]
Oct. 31, 2011
PSUs [Member]
Executive Officer [Member]
Oct. 31, 2012
Restricted Stock Units (RSUs) [Member]
Oct. 31, 2011
Restricted Stock Units (RSUs) [Member]
Oct. 31, 2012
2004 Incentive Stock Plan [Member]
Oct. 31, 2012
Employee Stock Purchase Plan [Member]
Oct. 31, 2011
Employee Stock Purchase Plan [Member]
Oct. 31, 2011
Convertible Notes [Member]
Oct. 31, 2011
Convertible Notes [Member]
Oct. 31, 2012
Stock Options [Member]
Oct. 31, 2011
Stock Options [Member]
Oct. 31, 2012
Stock Options [Member]
Oct. 31, 2011
Stock Options [Member]
Stockholders' Equity (Textual) [Abstract]                                              
Number of common stock issuable with antidilutive effect                                   3,077,995 2,568,098 163,542 2,431,906 229,639 2,431,906
Percentage of common stock authorized                             15.00%                
Authorized of common stock                             10,000,000                
Period to award vested and calculate volatility rate 3 years                           3 years                
Period of award vested exercisable                             10 years                
Exercise price per share $ 11.02 $ 3.12           $ 1.47                              
Option granted under ESPP                               92,476 234,418            
Option granted 3,500 1,094,100           500,000                              
Option outstanding 3,051,660 3,902,832 3,988,164 3,137,565       250,000                              
Expiration date of options outstanding               Dec. 06, 2014                              
Stock-based compensation expense           $ 2,000,000 $ 1,100,000     $ 143,000     $ 643,000                    
Amount of cancelled PSU Excluded from compensation Expenses   180,000                                          
Amount of share based compensation delivered                         51,000 3,000                  
Share based compensation delivered                         7,667 1,000                  
Stock-based compensation expense related to the loss on sale of our discontinued operations (798,000)       45,000                                    
Performance-based restricted stock units granted in period                     34,800 95,200 55,250 0                  
Other than options cancelled in period                 35,000 88,700     12,331                    
Unrecognized compensation cost                 2,000,000       2,000,000                    
Stockholders Equity (Additional Textual) [Abstract]                                              
Intrinsic value of stock vested 15,800,000 1,100,000                                          
Intrinsic value of stock exercisable 9,800,000 938,000                                          
Intrinsic value of stock exercised 5,100,000 216,000                                          
Unamortized fair value of outstanding options $ 1,600,000                                            
Unamortized fair value options recognized remaining vesting period 1 year 2 months 12 days                                            
Performance period 3 years                                            
Percentage of maximum aggregate award granted 200.00%                                            
Percentage of stock outperform in order for target award to be earned 10.00%                                            
Period for cost expected to be recognized over a weighted average remaining contractual term 1 year 8 months 12 days                                            
Exercise price per share $ 11.02 $ 3.12           $ 1.47