Income taxes (Details) (USD $)	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Components of income before income tax expense [Abstract]
U.S.	$ (21,334,000)	$ 325,882,000	$ 330,511,000
Foreign	(23,524,000)	911,806,000	1,007,225,000
Income (loss) before income tax expense (benefit)	(44,858,000)	1,237,688,000	1,337,736,000
Current [Abstract]
U.S. federal	20,134,000	222,012,000	162,020,000
State and local	(8,258,000)	26,984,000	23,574,000
Foreign	10,176,000	52,452,000	56,866,000
Total current	22,052,000	301,448,000	242,460,000
Deferred [Abstract]
U.S.	(33,959,000)	(41,970,000)	45,997,000
Foreign	(848,000)	(848,000)	2,509,000
Total deferred	(34,807,000)	(42,818,000)	48,506,000
Total	(12,755,000)	258,630,000	290,966,000
Reconciliation between provision for income taxes and expected federal income taxes at statutory rate [Abstract]
U.S. statutory rate (in hundredths)	35.00%	35.00%	35.00%
Effect of foreign operations (in hundredths)	(88.80%)	(16.10%)	(17.90%)
Research credit (in hundredths)	46.00%	(1.00%)	(1.00%)
State and local taxes, less federal tax benefit (in hundredths)	(16.90%)	1.40%	1.10%
Unrecognized tax benefit - audit settlement and statute expiration	54.70%	0.00%	0.00%
Government investigation (in hundredths)	0.00%	0.00%	2.10%
Permanent differences and other items (in hundredths)	(1.60%)	1.60%	2.50%
Total (in hundredths)	28.40%	20.90%	21.80%
Net deferred income taxes [Abstract]
Inventory reserves	42,924,000	42,121,000
Receivable allowances and other reserves	37,169,000	33,912,000
Plant, property and equipment	(24,302,000)	(12,759,000)
Intangible assets	(255,260,000)	(278,853,000)
Carryforwards and credits	64,378,000	57,740,000
Accrued liabilities	65,193,000	56,821,000
Employee stock option tax benefits	41,726,000	39,953,000
Other (includes reserve for legal contingencies)	21,169,000	29,398,000
Gross deferred taxes	(7,003,000)	(31,667,000)
Valuation allowance	(9,787,000)	(11,875,000)
Deferred taxes, net	(16,790,000)	(43,542,000)
Undistributed earnings of foreign subsidiaries	6,300,000,000
Number of months on outcome of IRS review	12 months
Unrecognized tax benefits that would impact effective tax rate	466,000,000
Reconciliation of beginning and ending amount of unrecognized tax benefits [Roll Forward]
Balance at beginning of period	498,292,000	426,398,000
Additions related to prior year positions	2,011,000	5,406,000
Reductions related to prior year positions	(1,630,000)	(874,000)
Reduction related to audit settlement	(7,806,000)	(13,177,000)
Reduction related to statute expiration	(11,500,000)	(6,530,000)
Additions related to current year positions	12,721,000	87,069,000
Balance at ending of period	492,088,000	498,292,000	426,398,000
Amount of tax interest and penalties	14,800,000	12,800,000
Amount of accrued interest related to unrecognized tax benefits	$ 75,200,000	$ 72,100,000
Number of months that unrecognized tax benefits is anticipated will not change	12 months