Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net loss	$ (9,597)	$ (27,970)
Adjustments for non-cash operating items:
Amortization of deferred revenue	(92,479)	(45,448)
Stock-based compensation	17,520	10,516
Amortization of debt discount and debt issuance costs	6,491
Depreciation on property and equipment	959	324
Accretion of discount on investment securities	(93)	(50)
Changes in operating assets and liabilities:
Receivables from collaboration partners	(4,537)	7,051
Prepaid expenses and other current assets	(1,981)	3,103
Other non-current assets	32	(3,411)
Accounts payable	(1,483)	2,082
Accrued expenses	24,603	5,747
Deferred revenue		3,000
Other current liabilities	243	(4,354)
Other non-current liabilities	4,285	(810)
Net cash used in operating activities	(56,037)	(50,220)
Cash flows from investing activities:
Purchases of short-term investments	(374,784)	(74,881)
Maturities of short-term investments	225,000	100,000
Purchases of property and equipment	(13,549)	(137)
Change in restricted cash	(3,697)
Net cash (used in) provided by investing activities	(167,030)	24,982
Cash flows from financing activities:
Proceeds from issuance of Convertible Notes, net	250,987
Financing transaction costs	(614)
Proceeds from stock option exercises	18,115	2,933
Net proceeds from stockholder securities law settlement		2,959
Net cash provided by financing activities	268,488	5,892
Net increase (decrease) in cash and cash equivalents	45,421	(19,346)
Cash and cash equivalents at beginning of period	70,136	107,717
Cash and cash equivalents at end of period	115,557	88,371
Non-cash investing and financing activities:
Property and equipment expenditures incurred but not yet paid	265
Performance share units withheld to satisfy tax withholding obligations not yet paid	$ 1,608