Income Taxes Components of deferred tax assets and liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Components of Deferred Tax Assets [Abstract]
Deferred intercompany profit	$ 9,623	$ 13,679
Deferred income on shipments to distributors	28,596	28,776
Inventory valuation	6,072	9,148
Net operating loss carryforward	110,598	77,959
Share-based compensation	24,494	27,757
Income tax credits	124,395	112,686
Accrued expenses and other	28,227	17,241
Gross deferred tax assets	332,005	287,246
Valuation allowances	(93,811)	(88,637)
Deferred tax assets, net of valuation allowances	238,194	198,609
Components of Deferred Tax Liabilities [Abstract]
Property, plant and equipment, principally due to differences in depreciation	(1,942)	(8,515)
Junior convertible debentures	(530,338)	(486,878)
Other	(13,740)	(10,779)
Deferred tax liabilities	546,020	506,172
Net deferred tax liability	(307,826)	(307,563)
Deferred Tax Assets, Net, Current	67,490	80,687
Deferred Tax Liabilities, Noncurrent	(375,316)	(388,250)
Net deferred tax liability	(307,826)	(307,563)
Unrecorded Tax Benefits Related to Share-Based Compensation	$ 29,800