Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock Private Placement	Common Stock At-the-market sales	Common Stock	Additional Paid-in Capital Private Placement	Additional Paid-in Capital At-the-market sales	Additional Paid-in Capital	Accumulated Deficit	Private Placement	At-the-market sales	Total
Balance at Dec. 31, 2018			$ 3			$ 261,722	$ (241,551)			$ 20,174
Balance (in shares) at Dec. 31, 2018			34,377,329
Increase (decrease) in stockholders' equity
Adjustment to derivative liabilities upon adoption of ASU 2017-11						213	(213)
Share-based compensation - stock options and RSUs						490				490
Issuance of common stock	$ 1			$ 7,809	$ 860			$ 7,810	$ 860
Issuance of common stock (in shares)	8,426,750	665,974
Vesting of RSUs (in shares)			145,204
Net loss							(4,669)			(4,669)
Balance at Mar. 31, 2019			$ 4			271,094	(246,433)			24,665
Balance (in shares) at Mar. 31, 2019			43,615,257
Balance at Dec. 31, 2019			$ 7			306,108	(260,370)			45,745
Balance (in shares) at Dec. 31, 2019			69,810,305
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs						621				621
Issuance of common stock	$ 2			$ 48,433				$ 48,435
Issuance of common stock (in shares)	17,250,000
Issuance of common stock upon exercise of options						119				119
Issuance of common stock upon exercise of options (in shares)			152,907
Warrant discount						3,570				3,570
Net loss							(7,883)			(7,883)
Balance at Mar. 31, 2020			$ 9			$ 358,851	$ (268,253)			$ 90,607
Balance (in shares) at Mar. 31, 2020			87,213,212