Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 298,139	$ 514,542
Marketable securities	978,473	1,176,115
Accounts receivable, net	684,242	584,603
Due from unconsolidated joint business	257,351	228,724
Inventory	337,619	326,843
Other current assets	122,126	144,600
Total current assets	2,677,950	2,975,427
Marketable securities	1,471,943	1,416,737
Property, plant and equipment, net	1,617,459	1,571,387
Intangible assets, net	1,783,981	1,608,191
Goodwill	1,193,279	1,146,314
Investments and other assets	368,937	331,548
Total assets	9,113,549	9,049,604
Current liabilities:
Current portion of notes payable and line of credit	453,361	3,292
Taxes payable	50,066	45,939
Accounts payable	173,330	186,448
Accrued expenses and other	660,562	677,210
Total current liabilities	1,337,319	912,889
Notes payable, line of credit and other financing arrangements	626,012	1,060,808
Long-term deferred tax liability	324,264	248,644
Other long-term liabilities	517,406	400,276
Total liabilities	2,805,001	2,622,617
Commitments and contingencies
Biogen Idec Inc. shareholders' equity
Preferred stock, par value $0.001 per share
Common stock, par value $0.0005 per share	129	128
Additional paid-in capital	4,217,248	4,185,048
Accumulated other comprehensive income (loss)	(17,710)	(26,535)
Retained earnings	3,409,308	3,106,761
Treasury stock, at cost	(1,303,074)	(839,903)
Total Biogen Idec Inc. shareholders' equity	6,305,901	6,425,499
Noncontrolling interests	2,647	1,488
Total equity	6,308,548	6,426,987
Total liabilities and equity	$ 9,113,549	$ 9,049,604