CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net income	$ 323,925	$ 365,325	$ 395,281
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	283,171	278,298	189,139
Deferred income taxes	(60,425)	(32,811)	5,321
Share-based compensation expense related to equity incentive plans	71,420	58,596	53,787
Excess tax benefit from share-based compensation	(758)	(1,216)	(1,411)
Loss on retirement of junior convertible debentures	0	50,631	0
Amortization of debt discount on convertible debentures	48,022	14,791	8,970
Amortization of debt issuance costs	3,968	2,463	1,959
Losses on equity method investments	345	317	177
(Gains) losses on sale of assets	(960)	0	244
Loss on write-down of fixed assets	0	362	0
Impairment of intangible assets	629	1,881	350
Realized gain on available-for-sale investments	(13,727)	(18,469)	0
Realized gain on equity method investment	(2,225)	0	0
Impairment of available-for-sale investment	3,995	0	0
Amortization of premium on available-for-sale investments	9,044	9,949	10,754
Special (income) charges	(819)	0	(459)
Gain on shares of acquired company	0	0	(2,438)
Changes in operating assets and liabilities, excluding impact of acquisitions:
Increase in accounts receivable	(2,150)	(15,893)	(12,508)
Decrease (increase) in inventories	48,245	25,517	(18,500)
Increase (Decrease) in Deferred Income	16,962	18,330	8,846
Decrease in accounts payable and accrued liabilities	(20,836)	(33,992)	(11,633)
Change in other assets and liabilities	36,657	(2,897)	48,685
Net cash provided by operating activities	744,483	721,182	676,564
Cash flows from investing activities:
Purchases of available-for-sale investments	(1,573,867)	(959,318)	(1,337,482)
Sales and maturities of available-for-sale investments	2,824,231	1,097,065	951,296
Sale of equity method investment	2,667	0	0
Acquisition of Micrel, net of cash acquired	(343,928)	0	0
Acquisition of ISSC, net of cash acquired	0	(252,469)	0
Purchase of additional controlling interest in ISSC	(18,051)	(32,095)	0
Acquisition of Supertex, net of cash acquired	0	(375,365)	0
Other business acquisitions, net of cash acquired	0	0	(11,187)
Investments in other assets	(7,056)	(6,663)	(9,069)
Proceeds from sale of assets	14,296	0	16,235
Capital expenditures	(97,895)	(149,472)	(113,072)
Net cash provided by (used in) investing activities	800,397	(678,317)	(503,279)
Cash flows from financing activities:
Payments to retire junior convertible debentures	0	(1,134,621)	0
Proceeds from issuance of senior convertible debentures	0	1,725,000	0
Repayments of revolving loan under previous credit facility	0	0	(650,000)
Repayments of revolving loan under new credit facility	(1,614,452)	(1,697,642)	(453,500)
Proceeds from borrowings on revolving loan under previous credit facility	0	0	30,000
Proceeds from borrowings on revolving loan under new credit facility	2,204,500	1,859,594	753,500
Proceeds from issuance of long-term borrowings	0	0	350,000
Repayments of long-term borrowings	0	(350,000)	0
Deferred financing costs	(2,156)	(32,846)	(7,515)
Payment of cash dividends	(291,087)	(286,478)	(281,204)
Repurchase of common stock	(363,829)	0	0
Proceeds from sale of common stock	28,718	34,433	60,086
Tax payments related to shares withheld for vested restricted stock units	(21,720)	(19,504)	(22,640)
Contingent consideration payment	0	0	(14,700)
Capital lease payments	(676)	(604)	(454)
Excess tax benefit from share-based compensation	758	1,216	1,411
Net cash (used in) provided by financing activities	(59,944)	98,548	(235,016)
Effect of foreign exchange rate changes on cash and cash equivalents	0	(201)	0
Net increase (decrease) in cash and cash equivalents	1,484,936	141,212	(61,731)
Cash and cash equivalents at beginning of period	607,815	466,603	528,334
Cash and cash equivalents at end of period	$ 2,092,751	$ 607,815	$ 466,603