Condensed Consolidated Statements of Income (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Revenues:
Product, net	$ 2,172,322	$ 1,742,765
Unconsolidated joint business	330,611	296,885
Other	52,030	90,101
Total revenues	2,554,963	2,129,751
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	312,431	279,245
Research and development	460,549	528,884
Selling, general and administrative	560,361	511,674
Amortization of acquired intangible assets	95,903	143,258
(Gain) loss on fair value remeasurement of contingent consideration	7,844	(799)
Total cost and expenses	1,437,088	1,462,262
Gain on sale of rights	0	3,859
Income from operations	1,117,875	671,348
Other income (expense), net	(14,986)	(5,601)
Income before income tax expense and equity in loss of investee, net of tax	1,102,889	665,747
Income tax expense	281,881	178,414
Equity in loss of investee, net of tax	834	7,605
Net income	820,174	479,728
Net income (loss) attributable to noncontrolling interests, net of tax	(2,367)	(228)
Net income attributable to Biogen Inc.	$ 822,541	$ 479,956
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 3.50	$ 2.03
Diluted earnings per share attributable to Biogen Inc.	$ 3.49	$ 2.02
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	234,995	236,786
Diluted earnings per share attributable to Biogen Inc.	235,630	237,849