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		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 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)	69,667	71,896	69,571	72,634
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)	51,685	62,874	53,786	65,594
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)	17,201	6,342	14,913	4,155
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)	196	2,246	287	2,451
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)	585	434	585	434