Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
ASSETS
Cash and cash equivalents	$ 115,557	$ 70,136
Short-term investments	224,854	74,996
Receivables from collaboration partners	17,082	12,545
Restricted cash	843
Prepaid expenses and other current assets	13,015	10,512
Total current assets	371,351	168,189
Property and equipment, net	13,585	720
Restricted cash, net of current	8,843	5,489
Other non-current assets	5,206	719
Total assets	398,985	175,117
LIABILITIES AND STOCKHOLDERS' EQUITY
Accounts payable	4,320	5,588
Accrued expenses	50,165	24,014
Deferred revenue	29,024	59,762
Other current liabilities	513	270
Total current liabilities	84,022	89,634
Convertible Notes, net of unamortized discount of $65,670 at September 30, 2012	193,080
Deferred revenue, net of current	21,768	83,509
Other non-current liabilities	4,938	653
Total liabilities	303,808	173,796
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock, $0.01 par value per share; 1,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.01 par value per share; 170,000,000 shares authorized; 74,148,795 and 71,463,676 shares issued and outstanding at September 30, 2012 and December 31, 2011, respectively	742	357
Additional paid-in capital	354,329	251,242
Accumulated other comprehensive (loss) gain	(6)	13
Accumulated deficit	(259,888)	(250,291)
Total stockholders' equity	95,177	1,321
Total liabilities and stockholders' equity	$ 398,985	$ 175,117