Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Series B redeemable convertible preferred stock [Member]	Total
Balances at Dec. 31, 2015	$ 6,000	$ 375,230,000	$ (362,522,000)	$ 11,890,000	$ 12,714,000
Balances (in shares) at Dec. 31, 2015	588,291			7,527,853
Accretion of dividends on Series B redeemable convertible preferred stock		(365,000)		$ 365,000	(365,000)
Accretion to redemption value of Series B redeemable convertible preferred stock		(1,493,000)		1,493,000	(1,493,000)
Conversion of Series B redeemable convertible preferred stock to common stock, value	$ 2,000	10,627,000		$ (13,748,000)	10,629,000
Conversion of Series B redeemable convertible preferred stock to common stock, shares	235,902			(7,527,853)
Warrants issued for Novolytics assets (value)		204,000			204,000
Common stock issued in June 2016 financing, net of offering costs and warrants (value)	$ 2,000	2,632,000			2,634,000
Common stock issued in June 2016 financing, net of offering costs and warrants (shares)	212,766
Common stock issued in November 2016 financing, net of offering costs and warrants (value)	$ 5,000	680,000			685,000
Common stock issued in November 2016 financing, net of offering costs and warrants (shares)	533,500
Common stock issued pursuant to anti-dilution rights (value)	$ 1,000	1,544,000			1,545,000
Common stock issued pursuant to anti-dilution rights (shares)	75,020
Common stock issued under the employee stock purchase plan (value)		13,000			13,000
Common stock issued under the employee stock purchase plan (shares)	3,272
Stock-based compensation		1,995,000			1,995,000
Net loss			(18,838,000)		(18,838,000)
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 financing, net of offering costs (value)	$ 71,000	9,282,000			9,353,000
Common stock and pre-funded warrants issued in May 2017 financing, shares	7,067,419
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
Warrants exercised	$ 2,000	128,000			130,000
Warrants exercised (in shares)	226,664
Warrants reclassified from liabilities to equity due to exercise		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
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