Stock-Based Compensation - Early Exercise of Employee Options (Details) - Stock options - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jul. 31, 2019	Jul. 31, 2019	Jan. 31, 2019
Stock Based Compensation
Number of shares of common stock related to early exercised stock options subject to repurchase	1,316,192	1,316,192	545,941
Value of common stock related to early exercised stock options subject to repurchase	$ 10.5	$ 10.5	$ 1.2
Shares issued for exercise of stock options	1,037,356	1,037,356