Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Details) - shares	Jan. 31, 2016	Jan. 31, 2015
Class Of Stock [Line Items]
Shares underlying outstanding stock options	68,879,087	54,284,474
Shares reserved of common stock for future issuance	97,716,887
Employee Stock Purchase Plan
Class Of Stock [Line Items]
Shares reserved of common stock for future issuance	3,500,000
Equity Awards
Class Of Stock [Line Items]
Shares reserved of common stock for future issuance	25,337,800