Income Taxes Components of deferred tax assets and liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Mar. 31, 2011
Components of Deferred Tax Assets [Abstract]
Deferred intercompany profit	$ 14,624	$ 11,031
Deferred income on shipments to distributors	23,646	33,304
Inventory valuation	6,245	5,740
Net operating loss carryforward	33,639	2,884
Share-based compensation	25,693	25,195
Income tax credits	103,882	68,647
Accrued expenses and other	10,770	11,052
Gross deferred tax assets	218,499	157,853
Valuation allowances	(78,506)	(50,346)
Deferred tax assets, net of valuation allowances	139,993	107,507
Components of Deferred Tax Liabilities [Abstract]
Property, plant and equipment, principally due to differences in depreciation	(7,844)	(5,036)
Junior convertible debentures	(445,826)	(407,477)
Other	(6,500)	(5,699)
Deferred tax liabilities	460,170	418,212
Net deferred tax liability	(320,177)	(310,705)
Deferred Tax Assets, Net, Current	91,191	88,822
Deferred Tax Liabilities, Noncurrent	(411,368)	(399,527)
Net deferred tax liability	$ (320,177)	$ (310,705)