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Stock-based compensation and equity transactions - Additional Information (Detail) (USD $)
 3 Months Ended 6 Months Ended 3 Months Ended 6 Months Ended
Jan. 31, 2013
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2013
Incentive stock options
Apr. 30, 2013
Common Stock
Apr. 30, 2013
Stock Option
Apr. 30, 2012
Stock Option
Apr. 30, 2013
Stock Option
Apr. 30, 2013
Cost of Sales
Apr. 30, 2012
Cost of Sales
Apr. 30, 2013
Selling and general expenses
Apr. 30, 2012
Selling and general expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Weighted average fair value of stock options under Black-Scholes pricing model   $ 1.12 $ 1.33                  
Issuance of common stock for exercise of stock option         801,077     801,077        
Proceeds from exercise of stock options   $ 2,094,000 $ 76,000                  
Weighted average remaining life of options outstanding   3 years 3 months 29 days                    
Weighted average remaining contractual life of options exercisable   2 years 9 months 11 days                    
Weighted average life of options vested and expected to vest   3 years 3 months 26 days                    
Aggregate intrinsic value of options outstanding   4,900,000                    
Aggregate intrinsic value of options exercisable   3,700,000                    
Aggregate intrinsic value of options vested and expected to vest   3,800,000                    
Non-vested stock-based arrangements yet to be recognized   335,000                    
Stock based arrangements yet to be recognized, weighted average period expected to be recognized   3 years 11 days                    
Stock-based compensation expense   107,000 121,000     74,000 53,000   25,000 28,000 82,000 93,000
Non-employee director annual grant   25,000                    
Options granted for each non-employee director 8,405 4,367                    
Value of stock option issued $ 12,500 $ 7,292                    
Fair value of stock option $ 1.49 $ 1.67                    
Incentive stock options       138,280