STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities
Net loss	$ (221,760)	$ (104,468)	$ (67,830)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities
Depreciation and amortization	31,082	19,687	14,247
Non-cash compensation expense	56,094	39,897	31,259
Other non-cash charges and expenses, net	10,366	3,171	2,238
Changes in assets and liabilities
Increase in Sanofi and trade accounts receivable	(21,118)	(17,518)	(30,494)
Increase in prepaid expenses and other assets	(6,033)	(7,303)	(4,436)
(Decrease) increase in deferred revenue	(40,329)	158,151	(27,497)
Increase in accounts payable, accrued expenses, and other liabilities	50,016	7,605	12,577
Total adjustments	80,078	203,690	(2,106)
Net cash (used in) provided by operating activities	(141,682)	99,222	(69,936)
Cash flows from investing activities
Purchases of marketable securities	(240,391)	(605,124)	(199,997)
Sales or maturities of marketable securities	426,356	273,723	295,117
(Increase) decrease in restricted cash and marketable securities	(277)	(5,941)	50
Capital expenditures	(57,217)	(99,689)	(97,318)
Net cash provided by (used in) investing activities	128,471	(437,031)	(2,148)
Cash flows from financing activities
Proceeds in connection with facility lease obligation	0	47,544	23,640
Payments in connection with facility lease obligation	(674)	(924)	(875)
Payments in connection with capital lease obligation	(993)	(104)	0
Proceeds in connection with issuance of convertible notes, net of debt issuance costs	391,107	0	0
Proceeds in connection with issuance of warrants	93,800	0	0
Payment in connection with purchase of convertible note hedges	(117,500)	0	0
Net proceeds in connection with issuance of Common Stock	18,509	196,790	8,598
Net cash provided by financing activities	384,249	243,306	31,363
Net increase (decrease) in cash and cash equivalents	371,038	(94,503)	(40,721)
Cash and cash equivalents at beginning of period	112,572	207,075	247,796
Cash and cash equivalents at end of period	483,610	112,572	207,075
Supplemental disclosure of cash flow information
Cash paid for interest	$ 14,725	$ 12,737	$ 2,525