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Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (30,577)	$ (42,717)	$ (29,291)	$ (18,959)	$ (15,460)	$ (22,940)	$ (19,396)	$ (17,041)	$ (121,544)	$ (74,837)	$ (66,565)
Weighted-average common shares outstanding (in shares)									111,758,946	98,387,366	78,632,448
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.27)	$ (0.38)	$ (0.26)	$ (0.18)	$ (0.15)	$ (0.23)	$ (0.20)	$ (0.18)	$ (1.09)	$ (0.76)	$ (0.85)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common equivalent shares (in shares)									22,566,205	23,857,181	27,453,429
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common equivalent shares (in shares)									12,371,254	15,977,235	22,512,856
Restricted stock and restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common equivalent shares (in shares)									9,910,729	7,703,705	4,457,585
Shares committed under 2017 ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common equivalent shares (in shares)									284,222	176,241	482,988