Convertible Preferred Stock and Shareholders' Equity (Deficit) - Additional Information (Details) $ / shares in Units, $ in Thousands						1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Nov. 29, 2019 shares	May 29, 2019 shares	Nov. 29, 2018 shares	Jun. 14, 2018 USD ($) $ / shares shares	May 10, 2018	May 31, 2018 shares	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Class $ / shares shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 $ / shares shares
Class Of Stock [Line Items]
Number of classes of stock | Class									2
Capital stock, authorized shares				260,290,986			620,000,000		620,000,000
Common stock, shares authorized				153,944,895			600,000,000		600,000,000		153,945,000
Common stock, par value | $ / shares				$ 0.0001			$ 0.0001		$ 0.0001		$ 0.0001
Convertible preferred stock, shares authorized				106,346,091
Convertible preferred stock, par value | $ / shares				$ 0.0001
Preferred stock, shares authorized							20,000,000		20,000,000
Preferred stock, par value | $ / shares							$ 0.0001		$ 0.0001		$ 0.0001
Description of IPO transaction									There were no changes to the rights and preferences of the common stock as a result of the IPO.
Preferred stock converted into common stock				50,888,014
Convertible preferred stock, shares issued							0		0
Convertible preferred stock, shares outstanding							0		0
Fair value of shares repurchased | $									$ 1,738
Stock-based compensation cost | $							$ 4,343	$ 3,190	11,432	$ 9,015
Employees and Non-Employee Investors
Class Of Stock [Line Items]
Fair value of shares repurchased | $									$ 1,700
Tradestream Technologies Inc. and Wise 24 Inc
Class Of Stock [Line Items]
Common stock Issue						113,122
Tradestream Technologies Inc. and Wise 24 Inc | Scenario, Forecast
Class Of Stock [Line Items]
Common stock Issue	37,706	37,708	37,708
Common Stock
Class Of Stock [Line Items]
Preferred stock, conversion basis					2-to-1				2-to-1
Number of warrants net exercised to common stock							144,945		144,945
Common Stock Warrants
Class Of Stock [Line Items]
Number of warrants exercised				363,000
Proceeds from exercise of warrants | $				$ 3,700
Number of warrants outstanding							0		0
Common Stock Warrants | Board of Directors
Class Of Stock [Line Items]
Number of common stock warrants issued									80,000		80,000
Common stock warrants, weighted average exercise price, per share | $ / shares							$ 16.60		$ 16.60		$ 13.84
Common Stock Warrants | Board of Directors | General and Administrative
Class Of Stock [Line Items]
Stock-based compensation cost | $									$ 500	$ 500