Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 176,903	$ 138,236
Available for sale securities		2,012
Prepaid research and development expenses	596	1,020
Other current assets	419	247
Total current assets	177,918	141,515
Property and equipment, net	1,944	1,896
Other assets	37	34
Total assets	179,899	143,445
Current liabilities:
Accounts payable	1,401	3,036
Accrued research and development expenses	6,570	5,071
Other accrued expenses	1,876	2,889
Total current liabilities	9,847	10,996
Non-current liabilities	484	656
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock, par value $0.001 per share; 10,000,000 shares authorized, no shares issued and outstanding at June 30, 2012 and December 31, 2011
Common stock, $0.001 par value per share, 100,000,000 shares authorized at June 30, 2012 and December 31, 2011; 26,139,267 and 22,375,757 shares issued and outstanding at June 30, 2012 and December 31, 2011, respectively	26	22
Additional paid-in capital	314,650	242,221
Accumulated other comprehensive income	47	49
Deficit accumulated during development stage	(145,155)	(110,499)
Total stockholders' equity	169,568	131,793
Total liabilities and stockholders' equity	$ 179,899	$ 143,445