Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Condensed Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 387,141	$ 304,049	$ 689,507	$ 612,814
Other comprehensive income:
Unrealized gains (losses) on securities available for sale, net of tax of $47 and $621 for the three months ended June 30, 2012 and 2011, respectively; and $1,075 and $6,307 for the six months ended June 30, 2012 and 2011, respectively	(83)	1,057	1,828	(10,739)
Unrealized gains (losses) on foreign currency forward contracts, net of tax of $2,164 and $822 for the three months ended June 30, 2012 and 2011, respectively; and $22 and $1,213 for the six months ended June 30, 2012 and 2011, respectively	18,260	6,327	(103)	(11,050)
Unrealized gains (losses) on pension benefit obligation	202	4	391	16
Currency translation adjustment	(51,226)	22,235	(26,073)	74,784
Total other comprehensive income, net of tax	(32,847)	29,623	(23,957)	53,011
Comprehensive income	354,294	333,672	665,550	665,825
Comprehensive income attributable to noncontrolling interests, net of tax	295	18,933	65	36,137
Comprehensive income attributable to Biogen Idec Inc	$ 353,999	$ 314,739	$ 665,485	$ 629,688