Organization (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended	9 Months Ended
	Jul. 01, 2019	Jun. 25, 2018	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Organization
Payment of offering costs				$ 181	$ 2,971
Cash and cash equivalents			$ 114,214	$ 114,214		$ 150,637
Expected period of sufficient funds for planned operations				12 months
IPO
Organization
Common stock issued and sold in initial public offering (in shares)		7,359,998
Public offering price of the shares sold		$ 16.00
Net proceeds from issuance of common stock		$ 106,500
Payment of offering costs		$ 3,000
Number of preferred stock converted into common stock		20,306,497
New shares issued under the agreement		7,359,998
Underwriters' option
Organization
Common stock issued and sold in initial public offering (in shares)		959,999
New shares issued under the agreement		959,999
Sales Agreement
Organization
Common stock issued and sold in initial public offering (in shares)			0
Stock sale maximum aggregate offering price	$ 50,000
Stock sale commission percentage	3.00%
New shares issued under the agreement			0