Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 95,333	$ 104,713
Collaboration receivable	13	79
Prepaid expenses and other current assets	7,235	1,313
Total current assets	102,581	106,105
Property and equipment, net	2,108	1,141
Deposits	133	91
Other non-current assets	818	771
Total assets	105,640	108,108
Current liabilities:
Accounts payable	4,248	1,727
Accrued expenses	16,682	10,821
Deferred revenue - current portion	800	800
Deferred rent - current portion	6	15
Total current liabilities	21,736	13,363
Deferred revenue	2,933	3,533
Deferred rent	415	180
Warrant liabilities	21,528	19,425
Total liabilities	46,612	36,501
Commitments and contingencies (note 7)
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; 79,619,597 and 69,206,044 shares issued and outstanding at September 30, 2012 and December 31, 2011, respectively	80	69
Additional paid-in capital - common stock	305,538	246,519
Additional paid-in capital - warrants issued	6,909	12,611
Deficit accumulated during the development stage	(253,499)	(187,592)
Total stockholders' equity	59,028	71,607
Total liabilities and stockholders' equity	$ 105,640	$ 108,108