Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 451,723	$ 514,542
Marketable securities	1,154,071	1,176,115
Accounts receivable, net	661,519	584,603
Due from unconsolidated joint business	268,965	228,724
Inventory	392,936	326,843
Other current assets	126,174	144,600
Total current assets	3,055,388	2,975,427
Marketable securities	1,741,534	1,416,737
Property, plant and equipment, net	1,676,583	1,571,387
Intangible assets, net	1,681,232	1,608,191
Goodwill	1,204,740	1,146,314
Investments and other assets	271,144	331,548
Total assets	9,630,621	9,049,604
Current liabilities:
Current portion of notes payable and line of credit	453,209	3,292
Taxes payable	44,252	45,939
Accounts payable	157,424	186,448
Accrued expenses and other	866,208	677,210
Total current liabilities	1,521,093	912,889
Notes payable, line of credit and other financing arrangements	658,442	1,060,808
Long-term deferred tax liability	249,577	248,644
Other long-term liabilities	539,569	400,276
Total liabilities	2,968,681	2,622,617
Commitments and contingencies
Biogen Idec Inc. shareholders' equity
Preferred stock, par value $0.001 per share	0	0
Common stock, par value $0.0005 per share	127	128
Additional paid-in capital	3,819,063	4,185,048
Accumulated other comprehensive income (loss)	(51,115)	(26,535)
Retained earnings	4,194,551	3,106,761
Treasury stock, at cost	(1,303,074)	(839,903)
Total Biogen Idec Inc. shareholders' equity	6,659,552	6,425,499
Noncontrolling interests	2,388	1,488
Total equity	6,661,940	6,426,987
Total liabilities and equity	$ 9,630,621	$ 9,049,604