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	(16,525)
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)
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)
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)		80,523
Net loss	$ (43,047)
Ending balance (in shares) at Jun. 30, 2020	28,861,567	28,891,534	(29,967)
Ending balance at Jun. 30, 2020	$ 26,393	$ 29	$ (24)	231,593	(205,205)
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	28,861,567	28,891,534	(29,967)
Ending balance at Jun. 30, 2020	$ 26,393	$ 29	$ (24)	$ 231,593	$ (205,205)