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Stock-based compensation Fair value assumptions (Details)
6 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected volatility 40.88% 40.88%
Risk free interest rate 0.74% 0.74%
Dividend yield 0.00% 0.00%
Expected life 4 years 10 months 24 days 4 years 10 months 24 days
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected volatility 59.39% 60.26%
Risk free interest rate 1.77% 2.19%
Dividend yield 0.00% 0.00%
Expected life 5 years 1 month 12 days 5 years 1 month 12 days