Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Outstanding Stock Options
Balance, beginning of period (in shares)	15,977,235
Options granted (in shares)	0
Options exercised (in shares)	(3,307,708)
Options forfeited (in shares)	(298,273)
Balance, end of period (in shares)	12,371,254	15,977,235
Vested and expected to vest at end of period (in shares)	12,365,021
Exercisable at end of period (in shares)	10,249,816
Weighted-Average Exercise Price (in dollars per share):
Balance, beginning of period (in dollars per share)	$ 6.54
Options granted (in dollars per share)	0
Options exercised (in dollars per share)	4.49
Options forfeited (in dollars per share)	7.72
Balance, end of period (in dollars per share)	7.05	$ 6.54
Vested and expected to vest at end of period (in dollars per share)	7.05
Exercisable at end of period (in dollars per share)	$ 6.63
Weighted-Average Remaining Contractual Life (in years)	5 years 6 months 10 days	6 years 4 months 24 days
Vested and expected to vest at end of period, Weighted-Average Contractual Life (in years)	5 years 6 months 10 days
Exercisable at end of period, Weighted-Average Contractual Life (in years)	5 years 2 months 8 days
Aggregate Intrinsic Value	$ 98,028	$ 144,934
Vested and expected to vest at end of period, Aggregate Intrinsic Value	97,981
Exercisable at end of period, Aggregate Intrinsic Value	85,635
Options exercised, intrinsic value	$ 48,000	$ 79,400		$ 60,300
Options granted, weighted-average grant date fair value (in dollars per share)	$ 0		$ 5.79