Description of Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jul. 02, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Description Of Business [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
Common stock, shares authorized for issuance		200,000,000	200,000,000
Preferred stock, shares authorized for issuance		10,000,000	10,000,000
Preferred stock, par value per share		$ 0.01	$ 0.01
Cash and cash equivalents		$ 75,708	$ 104,583
Accumulated deficit		250,087	221,043
Cash flows from operating activities		30,482	$ 20,591	$ 11,144
$35.0 Million Credit Facility | Oxford Finance LLC
Description Of Business [Line Items]
Borrowings outstanding under credit facility		$ 30,000
Credit facility maturity date		Mar. 01, 2022
Common Stock
Description Of Business [Line Items]
Common stock shares issued and sold	6,325,000		6,325,000
Convertible preferred stock converted into common stock	11,000,000		10,994,000
Initial Public Offering
Description Of Business [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
Description Of Business [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