Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 19,371	$ 21,170
Available-for-sale investments	2,496	20,971
Prepaid expenses and other current assets	1,369	1,339
Total current assets	23,236	43,480
Property and equipment, net	263	259
Restricted cash	22	22
Other non-current assets		218
Total assets	23,521	43,979
Current liabilities:
Accounts payable	441	291
Accrued expenses	2,637	8,949
Total current liabilities	3,078	9,240
Total liabilities	3,078	9,240
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Common stock, $0.001 par value, 100,000,000 shares authorized at December 31, 2018 and 2017; 19,243,651 and 17,674,729 shares issued and outstanding at December 31, 2018 and 2017, respectively	19	18
Additional paid-in capital	209,366	202,953
Accumulated deficit	(210,470)	(189,741)
Accumulated other comprehensive income (loss)	5	(14)
Total stockholders’ equity	20,443	34,739
Total liabilities and stockholders’ equity	23,521	43,979
Series A Convertible Preferred Stock [Member]
Stockholders’ equity:
Preferred stock	$ 21,523	$ 21,523