Convertible Preferred Stock and Stockholders' Deficit - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	9 Months Ended
	Jul. 02, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Stockholders Deficit [Line Items]
IPO closing date	Jul. 02, 2018
Net proceeds from initial public offering			$ 99,998
Common stock, par value per share		$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized for issuance		200,000,000	200,000,000	200,000,000
Preferred stock, shares authorized for issuance		10,000,000	10,000,000	10,000,000
Preferred stock, par value per share		$ 0.01	$ 0.01	$ 0.01
Common stock, shares issued		17,579,000	17,579,000	231,000
Common stock, shares outstanding		17,579,000	17,579,000	231,000
Common Stock
Stockholders Deficit [Line Items]
Common stock shares issued and sold		6,325,000
Convertible preferred stock converted into common stock		10,994,000
Initial Public Offering
Stockholders Deficit [Line Items]
Net proceeds from initial public offering	$ 96,500
Common stock, par value per share	$ 0.01
Common stock, shares authorized for issuance	200,000,000
Preferred stock, shares authorized for issuance	10,000,000
Preferred stock, par value per share	$ 0.01
Initial Public Offering | Common Stock
Stockholders Deficit [Line Items]
Common stock shares issued and sold	6,325,000
Issuance price per share	$ 17.00
Convertible preferred stock converted into common stock	11,000,000