Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
At-the-market, offering expenses		$ 34	$ 67
Direct offering, common stock warrants		1,571
Direct offering, offering expenses		98
Pre-funded common stock warrants		1,875
Pre-funded common stock warrants offering expenses	$ 41	$ 93
Direct Placement Offering [Member]
Direct offering, offering expenses	93
Follow-on Public Offering One [Member]
Direct offering, offering expenses	7,132
Follow-on Public Offering Two [Member]
Direct offering, offering expenses	$ 8,770