Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues:
Product, net	$ 2,391,717	$ 2,117,366	$ 6,762,605	$ 5,916,423
Unconsolidated joint business	337,181	290,678	1,005,302	890,859
Other	48,961	103,402	156,557	255,367
Total revenues	2,777,859	2,511,446	7,924,464	7,062,649
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	310,028	302,639	908,579	873,771
Research and development	519,863	417,174	1,471,140	1,393,331
Selling, general and administrative	477,827	570,436	1,530,083	1,658,732
Amortization of acquired intangible assets	98,065	122,431	285,972	382,515
(Gain) loss on fair value remeasurement of contingent consideration	244	(49,433)	5,887	(46,213)
Total cost and expenses	1,406,027	1,363,247	4,201,661	4,262,136
Gain on sale of rights	0	4,379	0	12,138
Income from operations	1,371,832	1,152,578	3,722,803	2,812,651
Other income (expense), net	(15,413)	(16,290)	(41,288)	(17,030)
Income before income tax expense and equity in loss of investee, net of tax	1,356,419	1,136,288	3,681,515	2,795,621
Income tax expense	330,093	274,774	904,475	721,709
Equity in loss of investee, net of tax	6,833	5,394	12,548	14,932
Net income	1,019,493	856,120	2,764,492	2,058,980
Net income (loss) attributable to noncontrolling interests, net of tax	53,871	(738)	49,053	7,660
Net income attributable to Biogen Inc.	$ 965,622	$ 856,858	$ 2,715,439	$ 2,051,320
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 4.16	$ 3.63	$ 11.60	$ 8.67
Diluted earnings per share attributable to Biogen Inc.	$ 4.15	$ 3.62	$ 11.57	$ 8.64
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	232,191	236,217	234,134	236,641
Diluted earnings per share attributable to Biogen Inc.	232,612	236,972	234,659	237,449