Intangible Assets and Goodwill (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Goodwill [Line Items]
Income tax expense	$ 601,014,000	$ 470,554,000	$ 444,528,000
Accumulated impairment losses related to goodwill	0
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period	1,201,296,000	1,146,300,000
Increase to goodwill	35,700,000	48,200,000
Other goodwill adjustments		6,800,000
Goodwill, end of period	1,232,916,000	1,201,296,000	1,146,300,000
TECFIDERA
Goodwill [Line Items]
Income tax expense	1,500,000
Summary of roll forward of the changes in goodwill
Increase to goodwill	15,000,000
Fumapharm AG | TECFIDERA
Goodwill [Line Items]
Income tax expense	2,800,000
Summary of roll forward of the changes in goodwill
Increase to goodwill	25,000,000
One billion | Fumapharm AG
Goodwill [Line Items]
Cumulative sales level	$ 1,000,000,000