Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended					12 Months Ended
	Apr. 26, 2019	Sep. 30, 2020	Oct. 31, 2019	Apr. 30, 2019	Jul. 31, 2018	Aug. 31, 2017	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017	Aug. 08, 2017
Preferred stock, shares authorized								50,000,000
Preferred stock, shares issued								0
Preferred stock, shares outstanding								0
Common stock, shares authorized								750,000,000	750,000,000
Common stock, par value (in dollars per share)								$ 0.0001	$ 0.0001
Common stock, shares issued		4,791,665	5,714,286	5,263,158	4,500,000			86,223,000	78,005,000
Common stock, shares outstanding								86,223,000	78,005,000
Stock price (in dollars per share)		$ 60.00									$ 8.16
Issuance of common stock upon exercise of warrants (in shares)					332,896
Issuance of common stock upon exercise of warrants					$ 6,800		$ 6,762
Stock issued (in dollars per share)			$ 35	$ 19	$ 20
Payment of offering expenses	$ 600	$ 300	$ 400	$ 600	$ 500
Proceeds from issuance of common stock	$ 108,100	$ 271,000	$ 216,200	$ 108,100	$ 97,300
Option for additional shares
Common stock, shares issued	789,473		857,142		675,000
Common stock
Common stock, shares issued							62,083,000	86,223,000	78,005,000	54,040,000
Issuance of common stock in exchange for commitment to provide debt financing (in shares)						300,000,000
Issuance of common stock in exchange for commitment to provide debt financing						$ 2,400
Issuance of common stock upon exercise of warrants (in shares)							333,000