Consolidated Statements of Stockholders' Equity - USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Total
Balances at Dec. 31, 2016	$ 16,000	$ 391,067,000	$ (381,360,000)	$ 9,723,000
Balances (in shares) at Dec. 31, 2016	1,648,751
Cumulative effect adjustment from adoption of ASU 2016-09		8,000	(8,000)
Common stock and pre-funded warrants issued in May 2017 and October 2018 financing, net of offering costs (value)	$ 71,000	9,282,000		9,353,000
Common stock and pre-funded warrants issued in May 2017 and October 2018 financing, shares	7,067,419
Warrants exercised	$ 2,000	128,000		130,000
Warrants exercised (in shares)	226,664
Warrant derivative liability reclassified to equity due to exercise of warrants		119,000		119,000
Dilutive financing derivative liability reclassified to equity upon common stock issued pursuant to anti-dilution rights, value	$ 1,000	21,000		22,000
Dilutive financing derivative liability reclassified to equity upon common stock issued pursuant to anti-dilution rights, shares	28,684
Common stock issued pursuant to anti-dilution rights (value)	$ 5,000	514,000		519,000
Common stock issued pursuant to anti-dilution rights (shares)	523,210
Common stock issued under the employee stock purchase plan (value)		3,000		3,000
Common stock issued under the employee stock purchase plan (shares)	4,200
Stock-based compensation		700,000		700,000
Net loss			(12,838,000)	(12,838,000)
Balances at Dec. 31, 2017	$ 95,000	401,842,000	(394,206,000)	7,731,000
Balances (in shares) at Dec. 31, 2017	9,498,928
Common stock issued in registered public financings, net of offering costs (value)	$ 67,000	6,091,000		6,158,000
Common stock issued in registered public financings, net of offering costs (in shares)	6,743,640
Common stock and pre-funded warrants issued in May 2017 and October 2018 financing, net of offering costs (value)	$ 159,000	5,671,000		5,830,000
Common stock and pre-funded warrants issued in May 2017 and October 2018 financing, shares	15,825,000
Warrants exercised	$ 2,000	196,000		198,000
Warrants exercised (in shares)	217,400
Warrant derivative liability reclassified to equity due to exercise of warrants		184,000		184,000
Common stock issued under the employee stock purchase plan (value)		5,000		5,000
Common stock issued under the employee stock purchase plan (shares)	9,040
Stock-based compensation		478,000		478,000
Net loss			(12,110,000)	(12,110,000)
Balances at Dec. 31, 2018	$ 323,000	$ 414,467,000	$ (406,316,000)	$ 8,474,000
Balances (in shares) at Dec. 31, 2018	32,294,008