Organization and Description of Business - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended		9 Months Ended
	Oct. 22, 2018 USD ($) $ / shares shares	Oct. 31, 2018	Aug. 31, 2018 USD ($) $ / shares	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Organization and Description of Business [Line Item]
Reverse stock split description				The Company effected a 11.0634-for-1 reverse split of its outstanding common stock and redeemable convertible preferred stock.
Accumulated deficit				$ (118,043)	$ (99,065)
Net proceeds from the sale of redeemable convertible preferred stock				17,712
Cash and cash equivalents				24,300
Working capital				$ 17,300
Silicon Valley Bank
Organization and Description of Business [Line Item]
Term loan			$ 2,000
Series D
Organization and Description of Business [Line Item]
Net proceeds from the sale of redeemable convertible preferred stock			$ 17,700
Common stock,public offering price | $ / shares			$ 9.659
Subsequent Event | Initial Public Offering
Organization and Description of Business [Line Item]
Common stock, shares, issued and sold | shares	9,864,666
Common stock,public offering price | $ / shares	$ 5.00
Proceeds from issuance of initial public offering	$ 43,000
Subsequent Event | Common Stock
Organization and Description of Business [Line Item]
Reverse stock split conversion ratio		11.0634
Subsequent Event | Common Stock | Initial Public Offering
Organization and Description of Business [Line Item]
Redeemable convertible preferred stock | shares	13,225,114