Shares Excluded (Details) - shares shares in Thousands	3 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	82,660	71,560
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)	34,001	44,996
Unvested RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	23,846	18,999
Restricted stock subject to repurchase
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	2,632	1,685
Shares issuable pursuant to ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	297	470
Shares related to Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount (in shares)	21,884	5,410