Condensed Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance, Value at Dec. 31, 2018	$ 39	$ 428,059	$ (294,354)	$ (114)	$ 133,630
Balance, Shares at Dec. 31, 2018	39,547,558
Stock-based compensation expense		2,234			2,234
Shares issued upon exercise of stock options, Value		234			234
Shares issued upon exercise of stock options, Shares	17,291
Shares issued for consulting services		197			197
Shares issued for consulting services, Shares	10,195
Net loss			(21,960)		(21,960)
Other comprehensive income (loss)				187	187
Balance, Value at Mar. 31, 2019	$ 39	430,724	(316,314)	73	114,522
Balance, Shares at Mar. 31, 2019	39,575,044
Balance, Value at Dec. 31, 2019	$ 47	587,223	(400,727)	170	186,713
Balance, Shares at Dec. 31, 2019	46,720,225
Stock-based compensation expense		2,846			2,846
Shares issued upon exercise of stock options, Value		75			75
Shares issued upon exercise of stock options, Shares	7,500
Net loss			(28,922)		(28,922)
Other comprehensive income (loss)				(238)	(238)
Balance, Value at Mar. 31, 2020	$ 47	$ 590,144	$ (429,649)	$ (68)	$ 160,474
Balance, Shares at Mar. 31, 2020	46,727,725