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	1,370,992
Share-based compensation expense		541		541
Fair value of derivative warrant liability reclassified to additional paid-in capital		25,326		25,326
Issuance of common stock upon vesting of restricted stock units (in shares)	1,250
Issuance of common stock upon exercise of warrants		55		55
Issuance of common stock upon exercise of warrants (in shares)	5,478,002
Issuance of common stock in public offerings		3,338		3,338
Issuance of common stock in public offerings (in shares)	1,652,396
Issuance of common stock under ESPP		4		4
Issuance of common stock under ESPP (in shares)	1,133
Fractional shares issued due to reverse stock split	2,733
Issuance of common stock to 401(k) plan		6		6
Issuance of common stock to 401(k) plan (in shares)	440
Net loss			(20,898)	(20,898)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2018	$ 1	223,286	(204,805)	18,482
Ending Balance, (in shares) at Sep. 30, 2018	8,506,946
Stockholders' Equity Attributable to Parent, Beginning Balance at Jun. 30, 2018	$ 1	199,720	(201,630)	(1,909)
Beginning Balance, (in shares) at Jun. 30, 2018	4,077,667
Share-based compensation expense		85		85
Fair value of derivative warrant liability reclassified to additional paid-in capital		23,436		23,436
Issuance of common stock upon vesting of restricted stock units (in shares)	1,250
Issuance of common stock upon exercise of warrants		44		44
Issuance of common stock upon exercise of warrants (in shares)	4,427,084
Issuance of common stock in public offerings		1		1
Issuance of common stock in public offerings (in shares)	945
Issuance of common stock under ESPP (in shares)	945
Net loss			(3,175)	(3,175)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2018	$ 1	223,286	(204,805)	18,482
Ending Balance, (in shares) at Sep. 30, 2018	8,506,946
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2018	$ 1	223,440	(207,330)	$ 16,111
Beginning Balance, (in shares) at Dec. 31, 2018	9,309,255			9,309,255
Share-based compensation expense		203		$ 203
Issuance of common stock upon vesting of restricted stock units (in shares)	2,750
Issuance of common stock under ESPP		1		1
Issuance of common stock under ESPP (in shares)	1,065
Issuance of restricted common stock (in shares)	206,500
Net loss			(8,458)	(8,458)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2019	$ 1	223,644	(215,788)	$ 7,857
Ending Balance, (in shares) at Sep. 30, 2019	9,519,570			9,519,570
Stockholders' Equity Attributable to Parent, Beginning Balance at Jun. 30, 2019	$ 1	223,576	(213,109)	$ 10,468
Beginning Balance, (in shares) at Jun. 30, 2019	9,311,820
Share-based compensation expense		68		68
Issuance of common stock upon vesting of restricted stock units (in shares)	1,250
Issuance of common stock under ESPP (in shares)	0
Issuance of restricted common stock (in shares)	206,500
Net loss			(2,679)	(2,679)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2019	$ 1	$ 223,644	$ (215,788)	$ 7,857
Ending Balance, (in shares) at Sep. 30, 2019	9,519,570			9,519,570