v3.7.0.1
Common Stock and Stockholders' Equity - Stock Options (Detail) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended
Apr. 30, 2017
Jan. 31, 2017
Outstanding Stock Options    
Beginning Balance (in shares) 9,096,592  
Stock option grants (in shares) 0  
Stock options exercised (in shares) (625,290)  
Stock options canceled (in shares) (3,575)  
Ending Balance (in shares) 8,467,727  
Vested and expected to vest (in shares) 8,465,367  
Exercisable (in shares) 8,364,499  
Weighted- Average Exercise Price    
Beginning Balance (in dollars per share) $ 4.34  
Stock option grants (in dollars per share) 0.00  
Stock options exercised (in dollars per share) 3.60  
Stock options canceled (in dollars per share) 9.08  
Ending Balance (in dollars per share) 4.39  
Vested and expected to vest, Weighted-Average Exercise Price (in dollars per share) 4.39  
Exercisable, Weighted-Average Exercise Price (in dollars per share) $ 4.32  
Aggregate Intrinsic Value (in millions) $ 703 $ 716
Vested and expected to vest, Aggregate Intrinsic Value 703  
Exercisable, Aggregate Intrinsic Value $ 695