Convertible Preferred Stock and Stockholders'Equity (Deficit) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended	6 Months Ended		12 Months Ended
	Jan. 02, 2019	Nov. 30, 2018	Apr. 30, 2018	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock, shares authorized					200,000,000		200,000,000
Common stock, par or stated value per share					$ 0.001		$ 0.001
Preferred stock, shares authorized							10,000,000
Preferred stock, par value							$ 0.001
Proceeds from issuance of convertible preferred stock						$ 26,255
2018 Equity Incentive Plan
Class Of Stock [Line Items]
Common stock reserved for issuance	1,284,158	3,428,492
Shares of common stock available for issuance		87,111
Percentage of additional common shares reserved for issuance automatically increase on January 1 of each calendar year		4.00%
Share-based compensation, description					In addition, the number of shares of common stock available for issuance under the 2018 Plan will automatically increase on January 1 of each calendar year, starting on January 1, 2019 through January 1, 2028, in an amount equal to 4% of the total number of shares of the Company’s common stock on the last day of the calendar month before the date of each automatic increase, or a lesser number of shares determined by the Company’s board of directors.
Accrued liabilities, repurchase rights for early exercise of stock option					$ 1,000		$ 1,100
2018 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Common stock reserved for issuance	321,039	645,000
Shares of common stock available for issuance	750,000
Percentage of additional common shares reserved for issuance automatically increase on January 1 of each calendar year	1.00%
Share-based compensation, description					In addition, the number of shares of common stock available for issuance under the ESPP will automatically increase on January 1 of each calendar year, starting on January 1, 2019 through January 1, 2028, in an amount equal to the lesser of (i) 1% of the total number of shares of the Company’s common stock on the last day of the calendar month before the date of each automatic increase and (ii) 750,000 shares; provided that before the date of any such increase, the Company’s board of directors may determine that such increase will be less than the amount set forth in clauses (i) and (ii). On January 1, 2019, 321,039 shares were automatically added to the ESPP pursuant to the provision
Maximum percentage of eligible earnings withheld to purchase shares of common stock pursuant to ESPP		15.00%
Price of common stock purchased under ESPP as a percentage of fair value		85.00%
Number of shares issued under ESPP					26,430
Convertible Preferred Stock
Class Of Stock [Line Items]
Outstanding shares of convertible preferred stock converted into common stock, shares				8,118,108		8,118,108
Series C Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares issued		11,365,348	8,118,108
Proceeds from issuance of convertible preferred stock		$ 37,100	$ 26,300
IPO | Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock outstanding							26,737,354
IPO | Common Stock
Class Of Stock [Line Items]
Common stock issued, shares							13,699,636
Shares price, per share							$ 11.00
Proceeds from IPO, net of underwriting discounts and commissions and other offering costs							$ 137,500
Outstanding shares of convertible preferred stock converted into common stock, shares							16,687,477