Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Cash flows from operating activities:
Net loss	$ (5,060)	$ (17,926)
Adjustments for non-cash operating items:
Amortization of deferred revenue	(79,737)	(30,508)
Stock-based compensation	9,917	7,289
Amortization of debt discount and debt issuance costs	3,349
Depreciation on property and equipment	250	215
Accretion of discount on investment securities	(48)	(38)
Changes in operating assets and liabilities:
Receivables from collaboration partners	(1,956)	6,425
Prepaid expenses and other current assets	(1,982)	1,276
Other non-current assets	111	(1,874)
Accounts payable	314	3,056
Accrued expenses	17,300	2,802
Deferred revenue		3,000
Other current liabilities	(81)	(4,734)
Other non-current liabilities	1,862	(142)
Net cash used in operating activities	(55,761)	(31,159)
Cash flows from investing activities:
Purchases of short-term investments	(199,914)
Maturities of short-term investments	75,000	100,000
Purchases of property & equipment	(5,825)	(148)
Change in restricted cash	(816)
Net cash (used in) provided by investing activities	(131,555)	99,852
Cash flows from financing activities:
Proceeds from issuance of Convertible Notes, net	250,987
Financing transaction costs	(614)
Proceeds from stock option exercises	11,326	2,917
Net proceeds from stockholder securities law settlement		2,959
Net cash provided by financing activities	261,699	5,876
Net increase in cash and cash equivalents	74,383	74,569
Cash and cash equivalents at beginning of period	70,136	107,717
Cash and cash equivalents at end of period	144,519	182,286
Non-cash investing activities:
Property and equipment expenditures incurred but not yet paid	$ 6,220