Convertible Preferred Stock - Additional Information (Details) $ / shares in Units, $ in Thousands						1 Months Ended	12 Months Ended
	Apr. 02, 2018 USD ($) $ / shares shares	Nov. 06, 2017 USD ($) shares	Jul. 28, 2017 USD ($) $ / shares shares	Feb. 10, 2017 USD ($) $ / shares shares	Dec. 22, 2015 USD ($) $ / shares shares	Dec. 31, 2015 Tranche shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Feb. 09, 2017 USD ($)
Temporary Equity [Line Items]
Net proceeds from initial public offering after underwriting discounts and commissions and offering expenses | $							$ 150,843
Conversion of convertible preferred stock into common stock upon initial public offering, Shares	24,168,656
Proceeds from issuance of convertible preferred stock, net of issuance costs | $			$ 83,500
Changes in fair value of convertible preferred stock tranche liability | $								$ (876)
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized						62,269,145		62,304,354
Number of tranches | Tranche						2
Preferred stock shares issued				28,873,237	28,873,237			28,873,237
Issue price, per share | $ / shares				$ 0.71	$ 0.71
Proceeds from issuance of convertible preferred stock, net of issuance costs | $				$ 20,500	$ 20,500			$ 20,479
Issuance costs | $					$ 100
Convertible preferred stock, shares issued				28,873,237	4,522,670			62,269,144
Additional shares granted to purchase					28,873,237
Fair value of convertible preferred stock tranche liability | $					$ 6,200
Fair value of convertible preferred stock tranche liability remeasured | $				$ 5,100					$ 5,100
Series A Convertible Preferred Stock | Maximum
Temporary Equity [Line Items]
Issuance costs | $				$ 100
Series B Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized			64,930,561					64,930,561
Preferred stock shares issued								64,930,561
Issue price, per share | $ / shares			$ 1.44
Proceeds from issuance of convertible preferred stock, net of issuance costs | $		$ 10,000						$ 94,768
Issuance costs | $			$ 400
Convertible preferred stock, shares issued		6,944,445	57,986,116					64,930,561
Preferred stock estimated fair value | $		$ 11,700
Common Stock
Temporary Equity [Line Items]
Issuance of common stock in initial public offering, net of discounts and issuance costs, Shares							10,350,000
Net proceeds from initial public offering after underwriting discounts and commissions and offering expenses | $	$ 150,800
Conversion of convertible preferred stock into common stock upon initial public offering, Shares							24,168,656
Initial Public Offering
Temporary Equity [Line Items]
Issuance of common stock in initial public offering, net of discounts and issuance costs, Shares	10,350,000
Initial Public Offering | Common Stock
Temporary Equity [Line Items]
Issuance of common stock in initial public offering, net of discounts and issuance costs, Shares	10,350,000
Offering price | $ / shares	$ 16.00
Conversion of convertible preferred stock into common stock upon initial public offering, Shares	24,168,656