Statement of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance at Dec. 31, 2017	$ (192,652)		$ 2	$ 4,292	$ (196,946)
Beginning balance, shares at Dec. 31, 2017			231,000
Beginning balance at Dec. 31, 2017	$ 187,136	$ 187,136
Beginning balance, shares at Dec. 31, 2017	304,958,000	304,958,000
Exercises of stock options	$ 31		$ 1	30
Exercises of stock options, shares			20,000
Share-based compensation expense	144			144
Net loss	(5,497)				(5,497)
Ending balance at Mar. 31, 2018	(197,974)		$ 3	4,466	(202,443)
Ending balance, shares at Mar. 31, 2018			251,000
Ending balance at Mar. 31, 2018		$ 187,136
Ending balance, shares at Mar. 31, 2018		304,958,000
Beginning balance at Dec. 31, 2017	(192,652)		$ 2	4,292	(196,946)
Beginning balance, shares at Dec. 31, 2017			231,000
Beginning balance at Dec. 31, 2017	$ 187,136	$ 187,136
Beginning balance, shares at Dec. 31, 2017	304,958,000	304,958,000
Net loss	$ (17,954)
Ending balance at Sep. 30, 2018	$ 76,348		$ 176	291,072	(214,900)
Ending balance, shares at Sep. 30, 2018			17,579,000
Ending balance, shares at Sep. 30, 2018	0
Beginning balance at Mar. 31, 2018	$ (197,974)		$ 3	4,466	(202,443)
Beginning balance, shares at Mar. 31, 2018			251,000
Beginning balance at Mar. 31, 2018		$ 187,136
Beginning balance, shares at Mar. 31, 2018		304,958,000
Exercises of stock options	7			7
Exercises of stock options, shares			6,000
Share-based compensation expense	192			192
Net loss	(7,496)				(7,496)
Ending balance at Jun. 30, 2018	(205,271)		$ 3	4,665	(209,939)
Ending balance, shares at Jun. 30, 2018			257,000
Ending balance at Jun. 30, 2018		$ 187,136
Ending balance, shares at Jun. 30, 2018		304,958,000
Conversion of convertible preferred stock into common stock	187,136	$ (187,136)	$ 109	187,027
Conversion of convertible preferred stock into common stock, shares		(304,958,000)	10,994,000
Conversion of convertible preferred stock warrants into common stock warrants	1,874			1,874
Issuance of common stock in initial public offering, net of issuance costs of $3.464	96,535		$ 64	96,471
Issuance of common stock in initial public offering, net of issuance costs of $3.464, shares			6,325,000
Exercises of stock options	7			7
Exercises of stock options, shares			3,000
Share-based compensation expense	1,028			1,028
Net loss	(4,961)				(4,961)
Ending balance at Sep. 30, 2018	$ 76,348		$ 176	$ 291,072	$ (214,900)
Ending balance, shares at Sep. 30, 2018			17,579,000
Ending balance, shares at Sep. 30, 2018	0