Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
ASSETS
Cash and cash equivalents	$ 144,519	$ 70,136
Short-term investments	199,948	74,996
Receivables from collaboration partners	14,501	12,545
Prepaid expenses and other current assets	13,491	10,512
Total current assets	372,459	168,189
Property and equipment, net	12,525	720
Restricted cash	6,305	5,489
Other non-current assets	5,397	719
Total assets	396,686	175,117
LIABILITIES AND STOCKHOLDERS' EQUITY
Accounts payable	10,016	5,588
Accrued expenses	46,868	24,014
Deferred revenue	34,510	59,762
Other current liabilities	189	270
Total current liabilities	91,583	89,634
Convertible notes, net of unamortized discount of $68,567 at June 30, 2012	190,183
Deferred revenue, net of current	29,024	83,509
Other non-current liabilities	2,515	653
Total liabilities	313,305	173,796
Commitments and contingencies
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; 36,681,369 and 35,731,838 shares issued and outstanding at June 30, 2012 and December 31, 2011, respectively	367	357
Additional paid-in capital	338,362	251,242
Accumulated other comprehensive gain	3	13
Accumulated deficit	(255,351)	(250,291)
Total stockholders' equity	83,381	1,321
Total liabilities and stockholders' equity	$ 396,686	$ 175,117