Condensed Consolidated Statements of Income (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenues:
Product	$ 1,039,110	$ 975,757	$ 3,091,398	$ 2,839,562
Unconsolidated joint business	287,792	266,471	856,975	739,054
Other	58,652	67,706	150,147	143,308
Total revenues	1,385,554	1,309,934	4,098,520	3,721,924
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	139,358	123,527	411,666	327,143
Research and development	304,217	301,391	989,738	880,668
Selling, general and administrative	299,631	261,398	901,488	772,217
Collaboration profit sharing	75,545	81,475	239,951	244,319
Amortization of acquired intangible assets	53,013	49,347	151,256	157,699
Fair value adjustment of contingent consideration	9,456	2,500	23,573	5,900
Restructuring charge	803	1,803	2,225	18,390
Total cost and expenses	882,023	821,441	2,719,897	2,406,336
Gain on sale of rights	31,719	0	31,719	0
Income from operations	535,250	488,493	1,410,342	1,315,588
Other income (expense), net	(4,548)	(7,727)	13,546	(9,504)
Income before income tax expense and equity in loss of investee, net of tax	530,702	480,766	1,423,888	1,306,084
Income tax expense	131,044	127,104	334,213	339,608
Equity in loss of investee, net of tax	1,258	0	1,769	0
Net income	398,400	353,662	1,087,906	966,476
Net income attributable to noncontrolling interests, net of tax	0	1,836	0	32,286
Net income attributable to Biogen Idec Inc.	$ 398,400	$ 351,826	$ 1,087,906	$ 934,190
Net income per share:
Basic earnings per share attributable to Biogen Idec Inc.	$ 1.68	$ 1.45	$ 4.56	$ 3.85
Diluted earnings per share attributable to Biogen Idec Inc.	$ 1.67	$ 1.43	$ 4.53	$ 3.81
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Idec Inc.	236,474	242,883	238,331	242,266
Diluted earnings per share attributable to Biogen Idec Inc.	238,125	245,366	240,137	245,140