Common Stock - Schedule of Black-Scholes Option-pricing Model to Determine Fair Value of Shares Purchased under ESPP with Weighted Average Assumptions on Date of Grant (Details) - 2017 Employee Stock Purchase Plan	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	1.32%	0.00%	0.00%
Expected term (in years)	1 year 4 months 9 days
Expected volatility	45.74%	0.00%	0.00%
Dividend yield	0.00%	0.00%	0.00%