Condensed Consolidated Statements of Income (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues:
Product, net	$ 2,117,366	$ 1,453,554	$ 5,916,423	$ 3,935,251
Unconsolidated joint business	290,678	303,210	890,859	856,601
Other	103,402	71,016	255,367	174,497
Total revenues	2,511,446	1,827,780	7,062,649	4,966,349
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	302,639	234,696	873,771	599,173
Research and development	417,174	410,017	1,393,331	1,021,820
Selling, general and administrative	570,436	405,584	1,658,732	1,189,194
Amortization of acquired intangible assets	122,431	99,998	382,515	233,524
Collaboration profit sharing	0	0	0	85,357
(Gain) loss on fair value remeasurement of contingent consideration	(49,433)	(97)	(46,213)	(2,983)
Total cost and expenses	1,363,247	1,150,198	4,262,136	3,126,085
Gain on sale of rights	4,379	6,949	12,138	17,319
Income from operations	1,152,578	684,531	2,812,651	1,857,583
Other income (expense), net	(16,290)	(4,640)	(17,030)	(29,525)
Income before income tax expense and equity in loss of investee, net of tax	1,136,288	679,891	2,795,621	1,828,058
Income tax expense	274,774	186,105	721,709	410,753
Equity in loss of investee, net of tax	5,394	6,170	14,932	12,270
Net income	856,120	487,616	2,058,980	1,405,035
Net income (loss) attributable to noncontrolling interests, net of tax	(738)	0	7,660	0
Net income attributable to Biogen Idec Inc.	$ 856,858	$ 487,616	$ 2,051,320	$ 1,405,035
Net income per share:
Basic earnings per share attributable to Biogen Idec Inc.	$ 3.63	$ 2.06	$ 8.67	$ 5.93
Diluted earnings per share attributable to Biogen Idec Inc.	$ 3.62	$ 2.05	$ 8.64	$ 5.89
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Idec Inc.	236,217	237,070	236,641	237,131
Diluted earnings per share attributable to Biogen Idec Inc.	236,972	238,349	237,449	238,508