Condensed Consolidated Statements of Income (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Revenues:
Product, net	$ 1,742,765	$ 1,095,779
Unconsolidated joint business	296,885	264,606
Other	90,101	54,711
Total revenues	2,129,751	1,415,096
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	279,245	133,749
Research and development	528,884	284,340
Selling, general and administrative	511,674	352,598
Amortization of acquired intangible assets	143,258	51,301
Collaboration profit sharing	0	85,357
(Gain) loss on fair value remeasurement of contingent consideration	(799)	2,277
Total cost and expenses	1,462,262	909,622
Gain on sale of rights	3,859	5,051
Income from operations	671,348	510,525
Other income (expense), net	(5,601)	(14,457)
Income before income tax expense and equity in loss of investee, net of tax	665,747	496,068
Income tax expense	178,414	65,508
Equity in loss of investee, net of tax	7,605	3,811
Net income	479,728	426,749
Net income (loss) attributable to noncontrolling interests, net of tax	(228)	0
Net income attributable to Biogen Idec Inc.	$ 479,956	$ 426,749
Net income per share:
Basic earnings per share attributable to Biogen Idec Inc.	$ 2.03	$ 1.80
Diluted earnings per share attributable to Biogen Idec Inc.	$ 2.02	$ 1.79
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Idec Inc.	236,786	236,837
Diluted earnings per share attributable to Biogen Idec Inc.	237,849	238,304