Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues:
Product, net	$ 2,198,566	$ 2,056,292	$ 4,370,888	$ 3,799,057
Unconsolidated joint business	337,510	303,296	668,121	600,181
Other	55,566	61,864	107,596	151,965
Total revenues	2,591,642	2,421,452	5,146,605	4,551,203
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	286,120	291,887	598,551	571,132
Research and development	490,728	447,273	951,277	976,157
Selling, general and administrative	491,895	576,622	1,052,256	1,088,296
Amortization of acquired intangible assets	92,004	116,826	187,907	260,084
(Gain) loss on fair value remeasurement of contingent consideration	(2,201)	4,019	5,643	3,220
Total cost and expenses	1,358,546	1,436,627	2,795,634	2,898,889
Gain on sale of rights	0	3,900	0	7,759
Income from operations	1,233,096	988,725	2,350,971	1,660,073
Other income (expense), net	(10,889)	4,861	(25,875)	(740)
Income before income tax expense and equity in loss of investee, net of tax	1,222,207	993,586	2,325,096	1,659,333
Income tax expense	292,501	268,521	574,382	446,935
Equity in loss of investee, net of tax	4,881	1,933	5,715	9,538
Net income	924,825	723,132	1,744,999	1,202,860
Net income (loss) attributable to noncontrolling interests, net of tax	(2,451)	8,626	(4,818)	8,398
Net income attributable to Biogen Inc.	$ 927,276	$ 714,506	$ 1,749,817	$ 1,194,462
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 3.94	$ 3.02	$ 7.44	$ 5.05
Diluted earnings per share attributable to Biogen Inc.	$ 3.93	$ 3.01	$ 7.42	$ 5.03
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	235,286	236,661	235,122	236,729
Diluted earnings per share attributable to Biogen Inc.	235,718	237,401	235,671	237,634