CONDENSED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 17,454	$ 13,983
Marketable securities-short term	25,661	24,789
Prepaid expenses and other current assets	420	714
Total current assets	43,535	39,486
Property and equipment, net	228	266
Other assets	252	252
Total assets	44,015	40,004
Current liabilities:
Accounts payable and accrued expenses	6,235	6,234
Deferred revenue	2,301	4,591
Total current liabilities	8,536	10,825
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.01 par value; 1,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.01 par value; 100,000,000 shares authorized; 71,106,224 and 62,939,780 shares issued and outstanding at June 30, 2016 and December 31, 2015, respectively	711	629
Additional paid-in capital	526,934	510,664
Accumulated other comprehensive income	32	3
Accumulated deficit	(492,198)	(482,117)
Total stockholders' equity	35,479	29,179
Total liabilities and stockholders' equity	$ 44,015	$ 40,004