Common Stock - Schedule of Total Stock-Based Compensation Expense Recognized by Type of Award (Parenthetical) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Sep. 30, 2017	May 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Apr. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Non-cash adjustments	$ 700
Additional stock-based compensation expense			$ 51,818	$ 13,834	$ 9,755
Eligible Option
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Outstanding and unexercised stock option exercise price		$ 13.68
Eligible options shares of common stock repriced		3,291,783
Eligible options repriced common stock weighted average exercise price		$ 24.31
Additional stock-based compensation expense		$ 2,600	$ 7,300
Minimum
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Outstanding and unexercised stock option exercise price						$ 13.68