Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 68,204	$ 73,306
Receivables	145	58
Prepaid expenses and other current assets	1,948	6,912
Total current assets	70,297	80,276
Property and equipment, net	801	1,994
Deposits	128	133
Other non current assets	528	1,001
Total assets	71,754	83,404
Current liabilities:
Accounts payable	422	1,509
Accrued expenses	6,357	16,516
Deferred revenue-current portion	800	800
Deferred rent-current portion	212	39
Total current liabilities	7,791	18,864
Deferred revenue	1,933	2,733
Deferred rent	851	400
Warrant liabilities	11,776	12,962
Other long term liabilities	20	0
Total liabilities	22,371	34,959
Commitments and contingencies (note 8)
Stockholders' equity:
Preferred stock, $0.001 par value; 30,000,000 shares authorized and no shares issued and outstanding	0	0
Common stock, $0.001 par value; 250,000,000 shares authorized; 100,159,618 and 83,236,840 shares issued and outstanding at December 31, 2013 and 2012, respectively	100	83
Additional paid-in capital-common stock	386,511	325,177
Additional paid-in capital-warrants issued	3,603	6,909
Deficit accumulated during the development stage	(340,831)	(283,724)
Total stockholders' equity	49,383	48,445
Total liabilities and stockholders' equity	$ 71,754	$ 83,404