Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 21,170	$ 36,392
Available-for-sale investments	20,971	4,925
Prepaid expenses and other current assets	1,339	1,438
Total current assets	43,480	42,755
Property and equipment, net	259	372
Other non-current assets	240	393
Total assets	43,979	43,520
Current liabilities:
Accounts payable	291	556
Accrued expenses	8,949	4,523
Total current liabilities	9,240	5,079
Total liabilities	9,240	5,079
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred Stock	0	0
Common stock, $0.001 par value, 100,000,000 shares authorized at December 31, 2017 and 2016; 17,674,729 and 16,603,559 shares issued and outstanding at December 31, 2017 and 2016, respectively	18	17
Additional paid-in capital	202,953	198,201
Accumulated deficit	(189,741)	(159,777)
Accumulated other comprehensive loss	(14)
Total stockholders’ equity	34,739	38,441
Total liabilities and stockholders’ equity	43,979	43,520
Series A Convertible Preferred Stock [Member]
Stockholders’ equity:
Preferred Stock	$ 21,523