CONDENSED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 19,962	$ 13,983
Marketable securities-short term	27,680	24,789
Prepaid expenses and other current assets	829	714
Total current assets	48,471	39,486
Property and equipment, net	239	266
Other assets	252	252
Total assets	48,962	40,004
Current liabilities:
Accounts payable and accrued expenses	5,391	6,234
Deferred revenue	3,451	4,591
Total current liabilities	$ 8,842	$ 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; 71,062,822 and 62,939,780 shares issued and outstanding at March 31, 2016 and December 31, 2015, respectively	$ 711	$ 629
Additional paid-in capital	526,475	510,664
Accumulated other comprehensive income	32	3
Accumulated deficit	(487,098)	(482,117)
Total stockholders' equity	40,120	29,179
Total liabilities and stockholders' equity	$ 48,962	$ 40,004