Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Net income	$ 1,380,033	$ 1,234,428	$ 1,005,273
Other comprehensive income:
Unrealized gains (losses) recognized during the period, net of tax of $2,940, $133 and $6,345	5,080	(224)	10,775
Less: reclassification adjustment for gains (losses) included in net income, net of tax of $486, $7,155 and $5,656	(903)	(12,184)	(9,631)
Unrealized gains (losses) on securities available for sale, net of tax of $2,454, $7,288 and $689	4,177	(12,408)	1,144
Unrealized gains (losses) recognized during the period, net of tax of $1,396, $3,647 and $1,268	(11,808)	32,830	(9,767)
Less: reclassification adjustment for gains (losses) included in net income, net of tax of $3,360, $1,268 and $304	(31,713)	9,767	(1,502)
Unrealized gains (losses) on foreign currency forward contracts, net of tax of $4,756, $4,915 and $964	(43,521)	42,597	(11,269)
Unrealized gains (losses) on pension benefit obligation, net of tax	(12,656)	(9,280)	(1,942)
Currency translation adjustment	23,230	(25,834)	(60,039)
Total other comprehensive income (loss), net of tax	(28,770)	(4,925)	(72,106)
Comprehensive income	1,351,263	1,229,503	933,167
Comprehensive income attributable to noncontrolling interests, net of tax	65	37,161	(108,940)
Comprehensive income attributable to Biogen Idec Inc.	$ 1,351,328	$ 1,266,664	$ 824,227