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Net Income per Share Attributable to Common Stockholders - Potential Common Share Equivalents Excluded where the Inclusion would be Anti-dilutive (Detail)
3 Months Ended 6 Months Ended
Jul. 31, 2014
Jul. 31, 2013
Jul. 31, 2014
Jul. 31, 2013
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]        
Options to purchase shares not included in the computation of diluted net income per share because their inclusion would be anti-dilutive 826,772 3,911,313 700,903 11,136,748