Intangible Assets and Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Feb. 12, 2015	Dec. 31, 2014
Intangible assets
Total intangible assets, gross	$ 7,645,800		$ 7,645,800			$ 7,207,100
Accumulated Amortization	(3,464,600)		(3,464,600)			(3,178,600)
Intangible assets, net	4,181,245		4,181,245			4,028,507
Intangible Assets and Goodwill (Textual) [Abstract]
Amortization of acquired intangible assets	98,065	$ 122,431	285,972	$ 382,515
Accumulated impairment losses related to goodwill	0		0
Expected future amortization expense, 2015 (remaining three months)	94,300		94,300
Expected future amortization expense, 2016	348,800		348,800
Expected future amortization expense, 2017	318,600		318,600
Expected future amortization expense, 2018	291,000		291,000
Expected future amortization expense, 2019	275,100		275,100
Expected future amortization expense, 2020	269,100		269,100
Total	1,596,900		1,596,900
Out-licensed patents
Intangible assets
Cost	543,300		543,300			543,300
Accumulated Amortization	(499,900)		(499,900)			(481,700)
Net	43,400		$ 43,400			61,600
Out-licensed patents | Minimum
Intangible assets
Estimated life, (in years)			13 years
Out-licensed patents | Maximum
Intangible assets
Estimated life, (in years)			23 years
Developed technology
Intangible assets
Cost	3,005,300		$ 3,005,300			3,005,300
Accumulated Amortization	(2,523,800)		(2,523,800)			(2,396,800)
Net	481,500		$ 481,500			608,500
Developed technology | Minimum
Intangible assets
Estimated life, (in years)			15 years
Developed technology | Maximum
Intangible assets
Estimated life, (in years)			23 years
Developed technology | AVONEX
Intangible assets
Net	472,900		$ 472,900
Acquired and in-licensed rights and patents
Intangible assets
Cost	3,297,600		3,297,600			3,280,400
Accumulated Amortization	(440,900)		(440,900)			(300,100)
Net	2,856,700		$ 2,856,700			2,980,300
Acquired and in-licensed rights and patents | Minimum
Intangible assets
Estimated life, (in years)			3 years
Acquired and in-licensed rights and patents | Maximum
Intangible assets
Estimated life, (in years)			17 years
In-process research and development
Intangible assets
Indefinite lived intangible assets useful life			Indefinite until commercialization
Cost and Net	735,600		$ 735,600			314,100
Accumulated Amortization	0		$ 0			0
Impairment of IPR&D intangible asset		$ 16,200
In-process research and development | Out-licensed patents
Intangible assets
Total impairment charges				$ 50,900
Trademarks and trade names
Intangible assets
Indefinite lived intangible assets useful life			Indefinite
Cost and Net	64,000		$ 64,000			64,000
Accumulated Amortization	0		0			$ 0
Convergence Pharmaceuticals
Intangible assets
In-process research and development and other intangible assets					$ 424,600
Convergence Pharmaceuticals | In-process research and development
Intangible assets
In-process research and development and other intangible assets					$ 424,600
TYSABRI product | Acquired and in-licensed rights and patents
Intangible assets
Net	$ 2,797,500		$ 2,797,500