Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 575,140	$ 759,598
Marketable securities	944,381	448,146
Accounts receivable, net	581,052	605,329
Due from unconsolidated joint business	231,582	222,459
Inventory	310,934	289,066
Other current assets	194,199	215,822
Total current assets	2,837,288	2,540,420
Marketable securities	1,349,359	743,101
Property, plant and equipment, net	1,572,259	1,641,634
Intangible assets, net	1,659,114	1,772,826
Goodwill	1,146,314	1,146,314
Investments and other assets	237,870	248,198
Total assets	8,802,204	8,092,493
Current liabilities:
Current portion of notes payable, line of credit and other financing arrangements	3,422	137,153
Taxes payable	47,984	84,517
Accounts payable	159,197	162,529
Accrued expenses and other	674,743	665,923
Total current liabilities	885,346	1,050,122
Notes payable and line of credit	1,060,639	1,066,379
Long-term deferred tax liability	238,175	200,950
Other long-term liabilities	384,450	325,599
Total liabilities	2,568,610	2,643,050
Commitments and contingencies (Notes 2, 11, 16, 18 and 20)
Biogen Idec Inc. shareholders' equity:
Preferred stock, par value $0.001 per share
Common stock, par value $0.0005 per share	128	124
Additional paid-in capital	4,143,429	3,895,103
Accumulated other comprehensive income (loss)	7,571	(21,610)
Retained earnings	2,806,523	1,872,481
Treasury stock, at cost	(728,503)	(349,592)
Total Biogen Idec Inc. shareholders' equity	6,229,148	5,396,506
Noncontrolling interests	4,446	52,937
Total equity	6,233,594	5,449,443
Total liabilities and equity	$ 8,802,204	$ 8,092,493