Condensed Statement of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock and Common Warrants [Member]	Pre-funded Warrants and Common Warrants [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Common Stock [Member] Common Stock and Common Warrants [Member]	Common Stock [Member] Pre-funded Warrants and Common Warrants [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Common Stock and Common Warrants [Member]	Additional Paid-in Capital [Member] Pre-funded Warrants and Common Warrants [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]
Beginning balance at Dec. 31, 2018	$ 19,600			$ (273)	$ 15			$ 188,083			$ (5)	$ (168,493)	$ (273)
Beginning balance, shares at Dec. 31, 2018					14,748,475
Accounting Standards Update [Extensible List]				us-gaap:AccountingStandardsUpdate201602Member
Exercise of stock options	165							165
Exercise of stock options, shares					126,560
Stock-based compensation expense	563							563
Unrealized gain (loss) on investments	5										5
Net loss	(7,213)											(7,213)
Ending balance at Mar. 31, 2019	12,847				$ 15			188,811				(175,979)
Ending balance, shares at Mar. 31, 2019					14,875,035
Beginning balance at Dec. 31, 2018	19,600			$ (273)	$ 15			188,083			(5)	(168,493)	$ (273)
Beginning balance, shares at Dec. 31, 2018					14,748,475
Unrealized gain (loss) on investments	29
Net loss	(14,385)
Ending balance at Jun. 30, 2019	29,984				$ 28			213,083			24	(183,151)
Ending balance, shares at Jun. 30, 2019					27,810,358
Beginning balance at Mar. 31, 2019	12,847				$ 15			188,811				(175,979)
Beginning balance, shares at Mar. 31, 2019					14,875,035
Stock issued during period, value		$ 21,622	$ 2,203			$ 12	$ 1		$ 21,610	$ 2,202
Stock issued during period, shares						11,838,582	1,096,741
Stock-based compensation expense	460							460
Unrealized gain (loss) on investments	24										24
Net loss	(7,172)											(7,172)
Ending balance at Jun. 30, 2019	29,984				$ 28			213,083			24	(183,151)
Ending balance, shares at Jun. 30, 2019					27,810,358
Beginning balance at Dec. 31, 2019	$ 16,048				$ 28			214,148			7	(198,135)
Beginning balance, shares at Dec. 31, 2019	27,810,358				27,810,358
Stock issuance costs	$ (28)							(28)
Stock-based compensation expense	505							505
Unrealized gain (loss) on investments	(8)										(8)
Net loss	(6,748)											(6,748)
Ending balance at Mar. 31, 2020	9,769				$ 28			214,625			(1)	(204,883)
Ending balance, shares at Mar. 31, 2020					27,810,358
Beginning balance at Dec. 31, 2019	$ 16,048				$ 28			214,148			7	(198,135)
Beginning balance, shares at Dec. 31, 2019	27,810,358				27,810,358
Unrealized gain (loss) on investments	$ (9)
Net loss	(11,138)
Ending balance at Jun. 30, 2020	$ 16,654				$ 39			225,890			(2)	(209,273)
Ending balance, shares at Jun. 30, 2020	39,261,576				39,261,576
Beginning balance at Mar. 31, 2020	$ 9,769				$ 28			214,625			(1)	(204,883)
Beginning balance, shares at Mar. 31, 2020					27,810,358
Stock issuance costs	(1,186)							(1,186)
Stock issued during period, value	11,915				$ 11			11,904
Stock issued during period, shares					11,425,118
RSUs vested, net of shares retained for tax	(13)							(13)
RSUs vested, net of shares retained for tax, shares					26,100
Stock-based compensation expense	560							560
Unrealized gain (loss) on investments	(1)										(1)
Net loss	(4,390)											(4,390)
Ending balance at Jun. 30, 2020	$ 16,654				$ 39			$ 225,890			$ (2)	$ (209,273)
Ending balance, shares at Jun. 30, 2020	39,261,576				39,261,576