Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 12,485	$ 21,170
Available-for-sale investments	13,969	20,971
Prepaid expenses and other current assets	1,057	1,339
Total current assets	27,511	43,480
Property and equipment, net	219	259
Restricted cash	22	22
Other non-current assets	100	218
Total assets	27,852	43,979
Current liabilities:
Accounts payable	431	291
Accrued expenses	1,800	8,949
Total current liabilities	2,231	9,240
Total liabilities	2,231	9,240
Commitments and contingencies (Note 4)
Stockholders’ equity:
Preferred Stock	0	0
Common stock, $0.001 par value, 100,000,000 shares authorized at June 30, 2018 and December 31, 2017; 17,726,713 and 17,674,729 shares issued and outstanding at June 30, 2018 and December 31, 2017, respectively.	18	18
Additional paid-in capital	204,780	202,953
Accumulated deficit	(200,701)	(189,741)
Accumulated other comprehensive income (loss)	1	(14)
Total stockholders’ equity	25,621	34,739
Total liabilities and stockholders’ equity	27,852	43,979
Series A Convertible Preferred Stock [Member]
Stockholders’ equity:
Preferred Stock	$ 21,523	$ 21,523