Organization and Description of Business - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended
	Oct. 22, 2018 USD ($) $ / shares shares	Apr. 30, 2019 USD ($) $ / shares shares	Oct. 31, 2018	Mar. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Organization and Description of Business [Line Item]
Common stock, shares authorized				200,000,000	200,000,000
Common stock, par value | $ / shares				$ 0.001	$ 0.001
Preferred Stock, Shares Authorized				10,000,000	10,000,000
Preferred Stock, Par Value | $ / shares				$ 0.001	$ 0.001
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 | $				$ (130,204)	$ (122,911)
Cash and cash equivalents | $				51,914	$ 61,051	$ 10,766	$ 13,406
Working capital | $				$ 50,300
Common Stock
Organization and Description of Business [Line Item]
Reverse stock split conversion ratio			11.0634
Initial Public Offering
Organization and Description of Business [Line Item]
Common stock, shares, issued and sold	9,864,666
Common stock,public offering price | $ / shares	$ 5.00
Proceeds from issuance of initial public offering | $	$ 43,000
Redeemable convertible preferred stock	13,200,115
Common stock, shares authorized				200,000,000
Common stock, par value | $ / shares				$ 0.001
Preferred Stock, Shares Authorized				10,000,000
Preferred Stock, Par Value | $ / shares				$ 0.001
Initial Public Offering | Subsequent Event
Organization and Description of Business [Line Item]
Common stock, shares, issued and sold		4,124,475
Common stock,public offering price | $ / shares		$ 12.00
Proceeds from issuance of initial public offering | $		$ 46,200
Initial Public Offering | Common Stock
Organization and Description of Business [Line Item]
Redeemable convertible preferred stock	13,200,115