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Employee Benefits and Stock-Based Compensation - Weighted-Average Assumptions Used to Estimate Fair Value (Detail)	12 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Options to purchase ordinary shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	66.00%	65.00%	63.00%
Risk-free interest rate	0.91%	1.64%	1.79%
Expected term (years)	6 years 18 days	6 years 18 days	6 years 18 days
Dividend yield	0.00%	0.00%	0.00%
Employee stock purchase plan awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	51.00%
Risk-free interest rate	0.18%
Expected term (years)	11 months 9 days
Dividend yield	0.00%

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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