Stock-Based Compensation - Stock options - Summary (Details) - Stock options - $ / shares shares in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2019
Number of Shares
Options outstanding at beginning of period (in shares)	26,200	26,535	26,535
Granted (in shares)	168	880
Exercised (in shares)	(4,776)	(706)
Canceled (in shares)	(325)	(509)
Options outstanding at end of period (in shares)	21,267	26,200	21,267
Options vested and expected to vest at end of period (in shares)	21,267		21,267
Options exercisable at end of period (in shares)	10,810		10,810
Weighted-Average Exercise Price Per Share
Options outstanding at beginning of period (in dollars per share)	$ 4.21	$ 3.87	$ 3.87
Granted (in dollars per share)	34.00	14.65
Exercised (in dollars per share)	3.62	2.14
Canceled (in dollars per share)	5.06	7.34
Options outstanding at end of period (in dollars per share)	4.56	$ 4.21	4.56
Options vested and expected to vest at end of period (in dollars per share)	4.56		4.56
Options exercisable at end of period (in dollars per share)	$ 1.97		$ 1.97