CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income (loss)	$ 750,269	$ (221,760)	$ (104,468)
Adjustments to reconcile net income (loss) to net cash (used in) provided by operating activities:
Depreciation and amortization	36,940	31,082	19,687
Non-cash compensation expense	94,157	56,094	39,897
Non-cash interest expense	22,925	5,101	43
Other non-cash charges and expenses, net	34,049	6,224	4,037
Deferred taxes	(340,156)
Changes in assets and liabilites
Increase in Sanofi and trade accounts receivable	(590,085)	(21,118)	(17,518)
Increase in prepaid expenses and other assets	(52,616)	(6,992)	(8,212)
(Decrease) increase in deferred revenue	(41,077)	(40,329)	158,151
Increase in accounts payable, accrued expenses and other liabilities	10,979	50,016	7,605
Total adjustments	(824,884)	80,078	203,690
Net cash (used in) provided by operating activities	(74,615)	(141,682)	99,222
Cash flows from investing activities:
Purchases of marketable securities	(470,393)	(240,391)	(605,124)
Sales or maturities of marketable securities	439,209	426,356	273,723
Increase in restricted cash and marketable securities	(552)	(277)	(5,941)
Capital expenditures	(49,337)	(57,217)	(99,689)
Net cash(used in) provided by investing activities	(81,073)	128,471	(437,031)
Cash flows from financing activities:
Proceeds in connection with facility lease obligation			47,544
Payments in connection with facility and capital lease obligations	(2,203)	(1,667)	(1,028)
Proceeds in connection with issuance of convertible notes, net of debt issuance costs		391,107
Proceeds in connection with issuance of warrants		93,800
Payment in connection with purchase of convertible note hedges		(117,500)
Net proceeds from issuance of Common Stock	63,549	43,587	200,588
Payments in connection with Common Stock tendered for employee tax obligations	(163,300)	(25,078)	(3,798)
Excess tax benefit from stock-based compensation	4,308
Net cash (used in) provided by financing activities	(97,646)	384,249	243,306
Net (decrease) increase in cash and cash equivalents	(253,334)	371,038	(94,503)
Cash and cash equivalents at beginning of period	483,610	112,572	207,075
Cash and cash equivalents at end of period	230,276	483,610	112,572
Supplemental disclosure of cash flow information
Cash paid for interest	$ 21,946	$ 14,725	$ 12,737