Accounts Receivable (Details Textual) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2012 EUR (€)	Mar. 31, 2013 Italy [Member] USD ($)	Dec. 31, 2011 Italy [Member] EUR (€)
Accounts Receivable (Textual) [Abstract]
Payment terms of accounts receivable arising from product sales	30 to 90 days
Minimum term for accounts receivable	30 days
Maximum term for accounts receivable	90 days
Accounts receivable outstanding for greater than one year	$ 15.6	$ 11.8
Payment in case of any unfavorable determination received			30.7		30.7
Cumulative deferred revenue on sales				90.4
Deferred revenue on sales of TYSABRI made in Italy				$ 13.9