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Stock-Based Compensation - Weighted-Average Assumptions Used to Estimate Fair Value (Detail) (Options to purchase ordinary shares [Member])
3 Months Ended 6 Months Ended
Jul. 31, 2013
Jul. 31, 2012
Jul. 31, 2013
Jul. 31, 2012
Options to purchase ordinary shares [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Volatility 66.00% 66.00% 65.00% 66.00%
Risk-free interest rate 1.25% 0.81% 1.21% 0.94%
Expected term (years) 6 years 18 days 6 years 18 days 6 years 18 days 6 years 18 days
Dividend yield 0.00% 0.00% 0.00% 0.00%