Commitments and Contingences (Details Textual) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Business Acquisition, Contingent Consideration [Line Items]
Payment of contingent payment for acquisition	$ 25,000,000	$ 0
Increase to goodwill	131,900,000		35,700,000
Fumapharm AG [Member] | TECFIDERA [Member]
Business Acquisition, Contingent Consideration [Line Items]
Payment of contingent payment for acquisition	25,000,000
Increase to goodwill	150,000,000
One billion [Member] | Fumapharm AG [Member]
Business Acquisition, Contingent Consideration [Line Items]
Cumulative sales level	1,000,000,000.0		1,000,000,000
Two billion [Member] | Fumapharm AG [Member]
Business Acquisition, Contingent Consideration [Line Items]
Cumulative sales level	$ 2,000,000,000