Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Details) - shares	Jan. 31, 2019	Jan. 31, 2018
Class of Stock [Line Items]
Shares underlying outstanding equity awards (in shares)	35,465,543	46,359,949
Shares reserved for future equity awards (in shares)	74,494,496
Employee stock purchase plan
Class of Stock [Line Items]
Shares reserved for future equity awards (in shares)	1,318,558
Unvested restricted stock units
Class of Stock [Line Items]
Shares reserved for future equity awards (in shares)	21,917,550
Employee Stock Options
Class of Stock [Line Items]
Shares reserved for future equity awards (in shares)	15,792,845