Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 110,391	$ 104,713
Collaboration receivable		79
Prepaid expenses and other current assets	9,051	1,313
Total current assets	119,442	106,105
Property and equipment, net	1,982	1,141
Deposits	132	91
Other non-current assets	824	771
Total assets	122,380	108,108
Current liabilities:
Accounts payable	1,470	1,727
Accrued expenses	15,502	10,821
Deferred revenue - current portion	800	800
Deferred rent - current portion	4	15
Total current liabilities	17,776	13,363
Deferred revenue	3,133	3,533
Deferred rent	363	180
Warrant liabilities	25,472	19,425
Total liabilities	46,744	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
Common stock, $0.001 par value; 250,000,000 shares authorized; 79,625,290 and 69,206,044 shares issued and outstanding at June 30, 2012 and December 31, 2011, respectively	80	69
Additional paid-in capital - common stock	304,219	246,519
Additional paid-in capital - warrants issued	7,012	12,611
Deficit accumulated during the development stage	(235,675)	(187,592)
Total stockholders' equity	75,636	71,607
Total liabilities and stockholders' equity	$ 122,380	$ 108,108