Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
ASSETS
Cash and cash equivalents	$ 180,147	$ 70,136
Short-term investments	199,939	74,996
Receivables from collaboration partners	14,515	12,545
Prepaid expenses and other current assets	9,551	10,512
Total current assets	404,152	168,189
Property and equipment, net	3,744	720
Restricted cash	6,305	5,489
Other non-current assets	6,581	719
Total assets	420,782	175,117
LIABILITIES AND STOCKHOLDERS' EQUITY
Accounts payable	10,659	5,588
Accrued expenses	33,888	24,014
Deferred revenue	64,889	59,762
Other current liabilities	1,097	270
Total current liabilities	110,533	89,634
Convertible notes, net of unamortized discount of $71,298 at March 31, 2012	187,452
Deferred revenue, net of current	41,557	83,509
Other non-current liabilities	416	653
Total liabilities	339,958	173,796
Commitments and contingencies (Note 10)
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; 50,000,000 shares authorized; 36,209,696 and 35,731,838 shares issued and outstanding at March 31, 2012 and December 31, 2011, respectively	362	357
Additional paid-in capital	330,320	251,242
Accumulated other comprehensive (loss) gain	(7)	13
Accumulated deficit	(249,851)	(250,291)
Total stockholders' equity	80,824	1,321
Total liabilities and stockholders' equity	$ 420,782	$ 175,117