Commitments and Contingencies (Details Textual) (USD $)	12 Months Ended				12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2006 FUMADERM and BG-12 [Member]	Dec. 31, 2010 Biogen Idec Hemophilia [Member]	Dec. 31, 2011 Biogen Idec Hemophilia [Member]	Dec. 31, 2007 Biogen Idec Hemophilia [Member]	Dec. 31, 2011 Weston Facility [Member]	Dec. 31, 2011 San Diego Facility [Member]	Dec. 31, 2011 New Cambridge Leases [Member]	Jul. 14, 2011 New Cambridge Leases [Member]
Business Acquisition [Line Items]
Sale Leaseback Transaction Period In Years									15 years
Total minimum lease payments								$ 240,000,000
Fair value of contingent consideration	151,000,000	81,200,000	0				80,000,000
Milestone payment payable to Acorda Therapeutics, Inc. (Acorda)					40,000,000
Additional contingent payment for Biologic License						20,000,000
Additional contingent payment for marketing authorization						20,000,000
Amount paid in cash				220,000,000
Contingent payment achieved in first quarter				15,000,000
Commitments And Contingencies (Textual) [Abstract]
Lease Rent Expense which terminates at various dates	46,200,000	44,800,000	36,400,000
Future minimum rental commitments	675,100,000									340,000,000	340,000,000
Liabilities associated with uncertain tax positions	58,400,000
Funding commitments, Approximately	14,500,000
Accrued expenses	25,000,000
Cancellable future commitments	475,000,000
Potential future milestone payments commitment, approximately	$ 1,900,000,000