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Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2018
Earnings Per Share [Abstract]
Net loss	$ (32,159)	$ (39,620)	$ (99,886)	$ (80,463)	$ (99,886)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	147,930	127,715	142,179	67,735
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.22)	$ (0.31)	$ (0.70)	$ (1.19)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	53,180	56,818	53,180	56,818
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	28,502	46,466	28,502	46,466
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	9,690	9,659	9,690	9,659
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	377	686	377	686
Unvested early exercises subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	7	0	7
Convertible senior notes (if-converted)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	14,611	0	14,611	0