Commitments and Contingences (Details Textual) (USD $)	3 Months Ended				3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 TECFIDERA [Member]	Dec. 31, 2006 Fumapharm AG [Member]	Mar. 31, 2013 Fumapharm AG [Member] TECFIDERA [Member]
Business Acquisition, Contingent Consideration [Line Items]
Amount paid in cash				$ 220,000,000
Additional payment if a Fumapharm Product is approved				15,000,000
Contingent payment					15,000,000
Tax benefit	$ 65,508,000	$ 82,148,000	$ 1,500,000		$ 1,500,000