Condensed Consolidated Statements of Income (Unaudited) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Revenues:
Product	$ 975,757	$ 876,850	$ 2,839,562	$ 2,560,305
Unconsolidated joint business	266,471	257,981	739,054	819,281
Other	67,706	40,958	143,308	117,765
Total revenues	1,309,934	1,175,789	3,721,924	3,497,351
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	123,527	95,918	327,143	299,958
Research and development	301,391	319,054	880,668	957,759
Selling, general and administrative	261,398	244,160	772,217	755,147
Collaboration profit sharing	81,475	63,991	244,319	190,240
Amortization of acquired intangible assets	49,347	53,531	157,699	155,568
Acquired in-process research and development		205,000		244,976
Restructuring charge	1,803		18,390
Fair value adjustment of contingent consideration	2,500		5,900
Total cost and expenses	821,441	981,654	2,406,336	2,603,648
Income from operations	488,493	194,135	1,315,588	893,703
Other income (expense), net	(7,727)	(6,945)	(9,504)	(14,318)
Income before income tax expense	480,766	187,190	1,306,084	879,385
Income tax expense	127,104	75,011	339,608	252,564
Net income	353,662	112,179	966,476	626,821
Net income (loss) attributable to noncontrolling interests, net of tax	1,836	(141,936)	32,286	(138,174)
Net income attributable to Biogen Idec Inc.	$ 351,826	$ 254,115	$ 934,190	$ 764,995
Net income per share:
Basic earnings per share attributable to Biogen Idec Inc.	$ 1.45	$ 1.06	$ 3.85	$ 2.98
Diluted earnings per share attributable to Biogen Idec Inc.	$ 1.43	$ 1.05	$ 3.81	$ 2.95
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Idec Inc.	242,883	239,864	242,266	256,586
Diluted earnings per share attributable to Biogen Idec Inc.	245,366	242,313	245,140	258,906