Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Total
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2017	$ 1	$ 194,016	$ (183,907)	$ 10,110
Beginning Balance, (in shares) at Dec. 31, 2017	45,700
Share-based compensation expense		618		618
Fair value of derivative warrant liability reclassified to additional paid-in capital		25,327		$ 25,327
Issuance of common stock upon vesting of restricted stock units (in shares)	143			143
Issuance of common stock under ESPP		4		$ 4
Issuance of common stock under ESPP (in shares)	48
Fractional shares issued due to reverse stock split	92
Issuance of common stock upon exercise of warrants		131		131
Issuance of common stock upon exercise of warrants (in shares)	209,246
Issuance of common stock and warrants in public offerings		3,338		3,338
Issuance of common stock and warrants in public offerings (in shares)	55,084
Issuance of common stock to 401(k) plan		6		6
Issuance of common stock to 401(k) plan (in shares)	17
Net loss			(23,423)	(23,423)
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 31, 2018	$ 1	223,440	(207,330)	$ 16,111
Ending Balance, (in shares) at Dec. 31, 2018	310,330			310,330
Share-based compensation expense		268		$ 268
Issuance of common stock upon vesting of restricted stock units (in shares)	143
Issuance of restricted common stock (in shares)	6,886
Issuance of common stock under ESPP		1		1
Issuance of common stock under ESPP (in shares)	36
Issuance of common stock and warrants in public offerings	$ 1	366		367
Issuance of common stock and warrants in public offerings (in shares)	233,341
Increase in fair value attributable to warrant modifications		666		666
Net loss			(11,830)	(11,830)
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 31, 2019	$ 2	$ 224,741	$ (219,160)	$ 5,583
Ending Balance, (in shares) at Dec. 31, 2019	550,736			550,736