Income taxes (Details) (USD $)	12 Months Ended
	Mar. 31, 2011	Mar. 31, 2010	Mar. 31, 2009
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 57,140,000	$ 70,051,000	$ 112,311,000
Increases related to acquisitions	26,843,000
Decreases related to prior year tax positions	(48,428,000)	(25,492,000)	(49,967,000)
Increases related to current year tax positions	9,977,000	11,332,000	7,584,000
Increases related to prior year tax positions	379,000	1,249,000	123,000
Ending balance	45,911,000	57,140,000	70,051,000
Amount of accruals related to potential payment of interest on Company's uncertain tax positions	500,000
Amount of accruals related to potential payment of penalties on Company's uncertain tax positions	1,000,000
Current (benefit) expense [Abstract]
Federal	294,000	(4,358,000)	(38,836,000)
State	21,000	(436,000)	(3,888,000)
Foreign	22,877,000	6,981,000	8,689,000
Total current	23,192,000	2,187,000	(34,035,000)
Deferred taxes expense (benefit) [Abstract]
Federal	11,035,000	16,663,000	19,476,000
State	788,000	1,668,000	1,950,000
Foreign	(3,484,000)	290,000	(899,000)
Total deferred	8,340,000	18,621,000	20,527,000
Total	31,531,000	20,808,000	(13,508,000)
Tax benefit from equity incentive plan	7,500,000	3,700,000	7,600,000
Reconciliation on difference of provision for income taxes from the amount computed applying statutory federal tax rate [Abstract]
Computed expected income tax provision	161,244,000	83,235,000	81,228,000
State income taxes, net of federal benefits	1,746,000	915,000	1,295,000
Research and development tax credits	(3,691,000)	(1,500,000)	(2,732,000)
Foreign income taxed at lower than the federal rate	(103,373,000)	(53,390,000)	(43,452,000)
Tax benefit from IRS settlement	(24,395,000)	(8,452,000)	(16,880,000)
Release of tax reserves			(32,967,000)
Pretax income from foreign operations	390,900,000	201,200,000	195,100,000
Unremitted foreign earnings	1,539,800,000
One-time tax benefit from IRS settlement		8,500,000
Approximate percentage points decrease of effective tax rate from tax benefit received from IRS settlement (in hundredths)	5.30%	3.60%
Effective tax rate after tax benefit received (in hundredths)		8.80%
Amount recognized from one-time tax benefit related to Emergency Economic Stabilization Act of 2008	1,500,000		1,500,000
Deferred tax assets [Abstract]
Deferred intercompany profit	11,031,000	7,711,000
Deferred income on shipments to distributors	33,304,000	24,531,000
Inventory valuation	5,740,000	842,000
Net operating loss carryforward	2,051,000	4,995,000
Share-based compensation	25,195,000	30,316,000
Accrued expenses and other	11,052,000	9,512,000
Income tax credits	50,795,000	45,171,000
Gross deferred tax assets	139,168,000	123,078,000
Valuation allowances	(50,346,000)	(45,268,000)
Net deferred tax assets	88,822,000	77,810,000
Deferred tax liabilities [Abstract]
Income tax credits	17,852,000
Deferred Tax Liability Operating Loss Carryforwards	833,000
Property, plant and equipment, principally due to differences in depreciation	(5,036,000)	(3,861,000)
Junior convertible debentures	(407,477,000)	(372,252,000)
Other	(5,699,000)	(600,000)
Gross deferred tax liability	399,527,000	376,713,000
Net deferred tax liability	(310,705,000)	(298,903,000)
Approximate amount of net operating loss carryforward for federal income tax purposes	2,900,000
Net operating loss carryforward valuation allowance	2,100,000
Estimated tax effect of state tax credits	44,800,000
Estimated tax effect of U.S. foreign tax credits	3,700,000
Foreign tax credits valuation allowance	3,500,000
Alternative minimum tax net operating loss carryforwards	4,000,000
Aggregate dollar benefits derived from tax holiday	$ 20,900,000	$ 17,300,000	$ 6,400,000
Approximate amount of diluted net income per share from tax holiday benefit	$ 0.10	$ 0.09	$ 0.03