Intangible Assets and Goodwill (Details 1) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Goodwill [Line Items]
Tax benefit	$ 65,508,000	$ 82,148,000
Goodwill acquired during the period	13,500,000		48,200,000
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period	1,201,296,000	1,146,300,000	1,146,300,000
Goodwill acquired during the period	13,500,000		48,200,000
Other Goodwill Adjustments	(4,100,000)		6,800,000
Goodwill, end of period	1,210,718,000		1,201,296,000
TECFIDERA [Member]
Goodwill [Line Items]
Tax benefit	1,500,000
Goodwill acquired during the period	15,000,000
Summary of roll forward of the changes in goodwill
Goodwill acquired during the period	$ 15,000,000