Net Loss per Share Attributable to Common Stockholders - Summary of Weighted-average Outstanding Shares Excluded from Computation of Diluted Net Loss per Share Attributable to Common Stockholders (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	70,765	73,648	69,854	73,528
Stock options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	53,878	65,567	54,864	66,974
Restricted stock units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	15,710	4,682	13,759	3,046
Early exercised stock options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	279	2,446	333	2,555
Employee stock purchase plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	898	953	898	953