Condensed Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, Value at Dec. 31, 2017	$ 86,780	$ 33	$ 307,158	$ (220,341)	$ (70)
Balance, Shares at Dec. 31, 2017		32,662,255
Stock-based compensation expense	1,871		1,871
Shares issued upon exercise of stock options, Value	263		263
Shares issued upon exercise of stock options, Shares		37,688
Net loss	(16,767)			(16,767)
Other comprehensive income (loss)	(44)				(44)
Balance, Value at Mar. 31, 2018	72,103	$ 33	309,292	(237,108)	(114)
Balance, Shares at Mar. 31, 2018		32,699,943
Balance, Value at Dec. 31, 2018	133,630	$ 39	428,059	(294,354)	(114)
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	$ 114,522	$ 39	$ 430,724	$ (316,314)	$ 73
Balance, Shares at Mar. 31, 2019		39,575,044