Condensed Consolidated Statements of Changes in Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2018	$ 177	$ 428,878	$ (357,794)	$ 71,261
Balance (in shares) at Dec. 31, 2018	176,918,000
Changes in Stockholders' Equity (Deficit)
Exercise of stock options and warrants		23		23
Exercise of stock options and warrants (in shares)	15,000
Stock-based compensation expense and vesting of RSUs		2,025		2,025
Stock-based compensation expense and vesting of RSUs (in shares)	25,000
Net loss			(29,365)	(29,365)
Balance at Mar. 31, 2019	$ 177	430,926	(387,159)	43,944
Balance (in shares) at Mar. 31, 2019	176,958,000
Balance at Dec. 31, 2019	$ 203	464,491	(473,343)	(8,649)
Balance (in shares) at Dec. 31, 2019	203,453,000
Changes in Stockholders' Equity (Deficit)
Issued shares of common stock		(86)		$ (86)
Issued shares of common stock (in shares)	175,000			175,089
Exercise of stock options and warrants	$ 1	497		$ 498
Exercise of stock options and warrants (in shares)	754,000
Stock-based compensation expense and vesting of RSUs		1,869		1,869
Stock-based compensation expense and vesting of RSUs (in shares)	63,000
Net loss			(42,593)	(42,593)
Balance at Mar. 31, 2020	$ 204	$ 466,771	$ (515,936)	$ (48,961)
Balance (in shares) at Mar. 31, 2020	204,445,000