Inventory (Details 1) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Components of inventory
Total finished goods and work in process	$ 345,600,000	$ 243,000,000
Raw materials	101,800,000	83,800,000
Total inventory	447,373,000	326,843,000
AVONEX
Components of inventory
Total finished goods and work in process	144,000,000	113,300,000
TYSABRI
Components of inventory
Total finished goods and work in process	114,800,000	114,700,000
Other
Components of inventory
Total finished goods and work in process	$ 86,800,000	$ 15,000,000