Business Overview - Additional Information (Details) - USD ($)	1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2017	Jul. 31, 2017	Jun. 30, 2017	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Proceeds from initial public offering, net of underwriting discounts and commissions						$ 62,314,000	$ 0
Conversion of convertible preferred stock			7,382,007
Net loss				$ 37,925,000	$ 23,770,000	120,272,000	$ 80,253,000	$ 105,800,000	$ 101,000,000	$ 69,700,000
Gross proceeds related to sale of convertible preferred stock								$ 124,600,000
Line of credit facility, outstanding borrowings				50,000,000		50,000,000
Revolving Credit Facility and Term Loan
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Line of credit facility, outstanding borrowings				$ 69,000,000		$ 69,000,000
Common Stock | IPO
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued		8,572,000
Shares price		$ 7.00
Proceeds from initial public offering, net of underwriting discounts and commissions		$ 55,800,000
Underwriting discounts and commissions		$ 4,200,000
Conversion of convertible preferred stock		17,992,973				17,992,973
Common Stock | Over-allotment Option
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued	1,000,000
Shares price	$ 7.00
Proceeds from initial public offering, net of underwriting discounts and commissions	$ 6,500,000
Underwriting discounts and commissions	$ 500,000