Consolidated Balance Sheets (Unaudited) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Current assets:    
Cash and cash equivalents $ 162,479 $ 138,236
Available for sale securities    2,012
Prepaid research and development expenses 443 1,020
Other current assets 378 247
Total current assets 163,300 141,515
Property and equipment, net 1,981 1,896
Other assets 38 34
Total assets 165,319 143,445
Current liabilities:    
Accounts payable 2,123 3,036
Accrued research and development expenses 7,577 5,071
Other accrued expenses 2,331 2,889
Total current liabilities 12,031 10,996
Non-current liabilities 408 656
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 September 30, 2012 and December 31, 2011      
Common stock, $0.001 par value per share, 100,000,000 shares authorized at September 30, 2012 and December 31, 2011; 26,139,267 and 22,375,757 shares issued and outstanding at September 30, 2012 and December 31, 2011, respectively 26 22
Additional paid-in capital 316,222 242,221
Accumulated other comprehensive income 55 49
Deficit accumulated during development stage (163,423) (110,499)
Total stockholders' equity 152,880 131,793
Total liabilities and stockholders' equity $ 165,319 $ 143,445