Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 18,225	$ 21,170
Available-for-sale investments	7,987	20,971
Prepaid expenses and other current assets	871	1,339
Total current assets	27,083	43,480
Property and equipment, net	200	259
Restricted cash	22	22
Other non-current assets	100	218
Total assets	27,405	43,979
Current liabilities:
Accounts payable	385	291
Accrued expenses	2,149	8,949
Total current liabilities	2,534	9,240
Total liabilities	2,534	9,240
Commitments and contingencies (Note 4)
Stockholders’ equity:
Preferred stock
Common stock, $0.001 par value, 100,000,000 shares authorized at September 30, 2018 and December 31, 2017; 19,221,292 and 17,674,729 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	19	18
Additional paid-in capital	208,536	202,953
Accumulated deficit	(205,211)	(189,741)
Accumulated other comprehensive income (loss)	4	(14)
Total stockholders’ equity	24,871	34,739
Total liabilities and stockholders’ equity	27,405	43,979
Series A Convertible Preferred Stock [Member]
Stockholders’ equity:
Preferred stock	$ 21,523	$ 21,523