Organization (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Jun. 25, 2018	Jun. 07, 2018	Dec. 31, 2019	Dec. 31, 2018
Organization
Accumulated deficit			$ (162,900)
Cash and cash equivalents			$ 98,849	$ 150,637
Expected period of sufficient funds for planned operations			12 months
Payment of offering costs			$ 182	$ 3,012
Reverse stock split ratio		0.03625
Preferred stock, shares authorized			10,000,000	10,000,000
Preferred stock, par value (in dollars per share)			$ 0.01	$ 0.01
Preferred stock, shares issued			0	0
Preferred stock, shares outstanding			0	0
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
Underwriters' option
Organization
Common stock issued and sold in initial public offering (in shares)	959,999