CONDENSED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018		24,528,242	29,967
Beginning balance at Dec. 31, 2018	$ 50,927	$ 25	$ (24)	$ 173,837	$ (122,911)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock warrants	210			210
Exercises of stock options (in shares)		150
Exercise of stock options	0
Stock-based compensation	238			238
Net loss	(7,293)				(7,293)
Ending balance (in shares) at Mar. 31, 2019		24,528,392	29,967
Ending balance at Mar. 31, 2019	44,082	$ 25	$ (24)	174,285	(130,204)
Beginning balance (in shares) at Dec. 31, 2018		24,528,242	29,967
Beginning balance at Dec. 31, 2018	50,927	$ 25	$ (24)	173,837	(122,911)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(27,916)
Ending balance (in shares) at Sep. 30, 2019		28,782,811	29,967
Ending balance at Sep. 30, 2019	70,804	$ 29	$ (24)	221,626	(150,827)
Beginning balance (in shares) at Mar. 31, 2019		24,528,392	29,967
Beginning balance at Mar. 31, 2019	44,082	$ 25	$ (24)	174,285	(130,204)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock warrants	86			86
Issuance of common stock in public offering, net (in shares)		4,124,475
Issuance of common stock in public offering, net	46,277	$ 4		46,273
Exercises of stock options (in shares)		74,740
Exercise of stock options	126			126
Stock-based compensation	270			270
Net loss	(9,232)				(9,232)
Ending balance (in shares) at Jun. 30, 2019		28,727,607	29,967
Ending balance at Jun. 30, 2019	81,609	$ 29	$ (24)	221,040	(139,436)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercises of stock options (in shares)		55,204
Exercise of stock options	95			95
Stock-based compensation	491			491
Net loss	(11,391)				(11,391)
Ending balance (in shares) at Sep. 30, 2019		28,782,811	29,967
Ending balance at Sep. 30, 2019	$ 70,804	$ 29	$ (24)	221,626	(150,827)
Beginning balance (in shares) at Dec. 31, 2019	28,766,404	28,796,371	29,967
Beginning balance at Dec. 31, 2019	$ 59,978	$ 29	$ (24)	222,131	(162,158)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock warrants	7,925			7,925
Exercises of stock options (in shares)		14,236
Exercise of stock options	17			17
Stock-based compensation	471			471
Net loss	(14,905)				(14,905)
Ending balance (in shares) at Mar. 31, 2020		28,810,607	29,967
Ending balance at Mar. 31, 2020	$ 53,486	$ 29	$ (24)	230,544	(177,063)
Beginning balance (in shares) at Dec. 31, 2019	28,766,404	28,796,371	29,967
Beginning balance at Dec. 31, 2019	$ 59,978	$ 29	$ (24)	222,131	(162,158)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net (in shares)		561,848
Net loss	$ (68,190)
Ending balance (in shares) at Sep. 30, 2020	29,359,321	29,389,288	29,967
Ending balance at Sep. 30, 2020	$ 4,352	$ 29	$ (24)	234,695	(230,348)
Beginning balance (in shares) at Mar. 31, 2020		28,810,607	29,967
Beginning balance at Mar. 31, 2020	53,486	$ 29	$ (24)	230,544	(177,063)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net (in shares)		80,523
Issuance of common stock in public offering, net	473			473
Exercises of stock options (in shares)		404
Exercise of stock options	1			1
Stock-based compensation	575			575
Net loss	(28,142)				(28,142)
Ending balance (in shares) at Jun. 30, 2020		28,891,534	29,967
Ending balance at Jun. 30, 2020	26,393	$ 29	$ (24)	231,593	(205,205)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net (in shares)		481,325
Issuance of common stock in public offering, net	2,469			2,469
Exercises of stock options (in shares)		16,429
Exercise of stock options	24			24
Stock-based compensation	609			609
Net loss	$ (25,143)				(25,143)
Ending balance (in shares) at Sep. 30, 2020	29,359,321	29,389,288	29,967
Ending balance at Sep. 30, 2020	$ 4,352	$ 29	$ (24)	$ 234,695	$ (230,348)