CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities
Net income	$ 181,947	$ 178,385
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	131,809	98,462
Deferred income taxes	(4,497)	11,872
Share-based compensation expense related to equity incentive plans	28,594	27,656
Excess tax benefit from share-based compensation	(982)	0
Convertible debt derivatives - revaluation and amortization	46	(248)
Amortization of debt discount on convertible debentures	4,810	4,396
Amortization of debt issuance costs	1,088	872
Losses on equity method investments	67	361
Impairment of intangible assets	556	350
Amortization of premium on available-for-sale investments	5,066	5,568
Special charge	0	(237)
Changes In Operating Assets And Liabilities
Increase in accounts receivable	(29,429)	(693)
Decrease (increase) in inventories	32,052	(32,103)
Increase in deferred income on shipments to distributors	11,787	12,097
Decrease in accounts payable and accrued liabilities	(15,817)	(2,006)
Change in other assets and liabilities	10,737	20,191
Net cash provided by operating activities	357,834	324,923
Cash flows from investing activities
Purchases of available-for-sale investments	(350,598)	(715,765)
Sales and maturities of available-for-sale investments	547,037	370,806
Acquisition of ISSC, net of cash acquired	(252,469)	0
Purchase of additional controlling interest in ISSC	(1,765)	0
Acquisition of Supertex, net of cash acquired	(375,365)	0
Other business acquisitions, net of cash acquired	0	(2,174)
Investments in other assets	(3,659)	(2,951)
Proceeds from sale of assets	0	16,200
Capital expenditures	(83,372)	(55,206)
Net cash used in investing activities	(520,191)	(389,090)
Cash flows from financing activities:
Repayments of revolving loan under previous credit facility	0	(650,000)
Repayments of revolving loan under new credit facility	(308,500)	(70,000)
Proceeds from borrowings on revolving loan under previous credit facility	0	30,000
Proceeds from borrowings on revolving loan under new credit facility	632,875	360,000
Proceeds from issuance of long-term borrowings	0	350,000
Repayments of long-term borrowings	(8,750)	0
Deferred financing costs	0	(7,515)
Payment of cash dividends	(142,644)	(139,768)
Proceeds from sale of common stock	14,035	32,888
Tax payments related to shares withheld for vested restricted stock units	(10,306)	(10,692)
Contingent consideration payment	0	(14,700)
Capital lease payments	(298)	(178)
Excess tax benefit from share-based compensation	982	0
Net cash provided by (used in) financing activities	177,394	(119,965)
Effect of foreign exchange rate changes on cash and cash equivalents	(201)	0
Net increase (decrease) in cash and cash equivalents	14,836	(184,132)
Cash and cash equivalents at beginning of period	466,603	528,334
Cash and cash equivalents at end of period	$ 481,439	$ 344,202