Other Consolidated Financial Statement Detail (Details Textual) (USD $)	12 Months Ended				12 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Cambridge Leases	Dec. 31, 2012 Stromedix, Inc.	Mar. 08, 2012 Stromedix, Inc.	Dec. 31, 2011 Biogen Dompe SRL and Biogen Dompe Switzerland GmbH	Mar. 04, 2008 6.0% Senior notes due 2013
Business Acquisition
Derecognition of construction in progress assets				$ 161,500,000
Total purchase price allocated to IPR&D						219,200,000
Total purchase price allocated to goodwill	1,232,916,000	1,201,296,000	1,146,300,000			48,200,000
Contingent consideration obligation	$ 0	$ 122,200,000			$ 122,200,000		$ 38,800,000
Debt Instrument, Interest Rate, Stated Percentage								6.00%