Equity Incentive Plans - Restricted Stock Units (Details) - Restricted Stock Units - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Number of Restricted Stock Units Outstanding
Unvested, Beginning balance (in shares)				21,917,550
Granted (in shares)				10,889,807
Vested (in shares)				(6,910,339)
Forfeited (in shares)				(2,239,739)
Unvested, Ending balance (in shares)	21,917,550	23,657,279		23,657,279
Weighted-Average Grant Date Fair Value
Beginning balance (in dollars per share)				$ 17.94
Granted (in dollars per share)				19.35
Vested (in dollars per share)				17.21
Forfeited (in dollars per share)				18.76
Ending balance (in dollars per share)	$ 17.94	$ 18.72		$ 18.72
Aggregate Intrinsic Value	$ 392,515	$ 460,371		$ 460,371
Share-based compensation expense		41,000	$ 31,200	118,700	$ 87,100
Compensation not yet recognized		$ 405,800		$ 405,800
Compensation cost (in years)				2 years 10 months 24 days