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Intangible Assets and Goodwill (Details 1) (USD $) | 12 Months Ended
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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 |  |

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 + Details
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