Microchip Technology (MCHP) 10-Q 11 Aug 14 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information Document	3 Months Ended
	Jun. 30, 2014	Jul. 31, 2014
DEI Information [Abstract]	'	'
Entity Registrant Name	'MICROCHIP TECHNOLOGY INC	'
Entity Central Index Key	'0000827054	'
Current Fiscal Year End Date	'--03-31	'
Entity Filer Category	'Large Accelerated Filer	'
Document Type	'10-Q	'
Document Period End Date	30-Jun-14	'
Document Fiscal Year Focus	'2015	'
Document Fiscal Period Focus	'Q1	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	200,400,918

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (unaudited) (USD $)	Jun. 30, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
ASSETS	'	'
Cash and cash equivalents	$617,770	$466,603
Short-term investments	1,142,091	878,182
Accounts receivable, net	286,699	242,405
Inventories	264,505	262,725
Prepaid expenses	34,369	31,756
Deferred tax assets	70,926	67,490
Other current assets	33,991	20,238
Total current assets	2,450,351	1,969,399
Property, plant and equipment, net	569,908	531,967
Long-term investments	527,539	798,712
Goodwill	409,885	276,097
Intangible assets, net	498,079	445,499
Other assets	45,981	45,956
Total assets	4,501,743	4,067,630
LIABILITIES AND STOCKHOLDERS' EQUITY	'	'
Accounts payable	79,889	74,050
Accrued liabilities	115,718	96,731
Short-term borrowings	17,500	17,500
Deferred Income on Shipments to Distributors	146,583	147,798
Total current liabilities	359,690	336,079
Junior convertible debentures	374,227	371,873
Long-term line of credit	634,375	300,000
Long-term borrowings, net	327,076	331,385
Long-term income tax payable	144,549	179,966
Deferred tax liability	453,069	375,316
Other long-term liabilities	39,112	37,550
Stockholders' equity:	'	'
Preferred stock, $0.001 par value; authorized 5,000,000 shares; no shares issued or outstanding	0	0
Common stock, $0.001 par value; authorized 450,000,000 shares; 218,789,994 shares issued and 200,401,106 shares outstanding at June 30, 2014; 218,789,994 shares issued and 200,002,736 shares outstanding at March 31, 2014	200	200
Additional paid-in capital	1,245,191	1,244,583
Common stock held in treasury: 18,388,888 shares at June 30, 2014; 18,787,258 shares at March 31, 2014	-565,551	-577,382
Accumulated other comprehensive income	4,089	1,051
Retained earnings	1,485,716	1,467,009
Total stockholders' equity	2,169,645	2,135,461
Total liabilities and stockholders' equity	$4,501,743	$4,067,630

CONDENSED_CONSOLIDATED_BALANCE1

CONDENSED CONSOLIDATED BALANCE SHEETS CONDENSED CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) (USD $)	Jun. 30, 2014	Mar. 31, 2014
Preferred Stock, Par or Stated Value Per Share	$0.00	$0.00
Preferred Stock, Shares Authorized	5,000,000	5,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common Stock, Par or Stated Value Per Share	$0.00	$0.00
Common Stock, Shares Authorized	450,000,000	450,000,000
Common Stock, Shares, Issued	218,789,994	218,789,994
Common Stock, Shares, Outstanding	200,401,106	200,002,736
Treasury Stock, Shares	18,388,888	18,787,258

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF INCOME (unaudited) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2014		Jun. 30, 2013
Income Statement	'		'
Net sales	$528,876		$462,792
Cost of sales (1)	222,357	[1]	196,218	[1]
Gross profit	306,519		266,574
Operating expenses:	'		'
Research and development (1)	84,370	[1]	73,085	[1]
Selling, general and administrative (1)	69,255	[1]	65,710	[1]
Amortization of acquired intangible assets	36,644		27,677
Special charges	304		1,701
Total operating expenses	190,573		168,173
Operating income	115,946		98,401
Losses on equity method investments	-32		-260
Other income (expense):	'		'
Interest income	4,742		3,925
Interest expense	-13,678		-11,856
Other income, net	13		126
Income before income taxes	106,991		90,336
Income tax provision	17,082		11,757
Net income	89,909		78,579
Basic net income per common share	$0.45		$0.40
Diluted net income per common share	$0.40		$0.37
Dividends declared per common share	$0.36		$0.35
Basic common shares outstanding	200,187		196,950
Diluted common shares outstanding	224,527		212,266
Allocated Share-based Compensation Expense	$11,901		$11,254
[1]	Includes share-based compensation expense as follows:Cost of sales 2,055 1,969 Research and development 6,309 5,690 Selling, general and administrative 4,957 4,997

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF INCOME (PARENTHETICAL) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014		Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'
Allocated Share-based Compensation Expense	$11,901		$11,254
Cost of Sales [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'
Allocated Share-based Compensation Expense	2,055	[1]	1,969	[1]
Research and Development Expense [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'
Allocated Share-based Compensation Expense	6,309		5,690
Selling General And Administrative Member	'		'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'		'
Allocated Share-based Compensation Expense	$4,957		$4,997
[1]	During the three months ended JuneB 30, 2014, $1.7 million of share-based compensation expense was capitalized to inventory and $2.1 million of previously capitalized share-based compensation expenses in inventory was sold. During the three months ended JuneB 30, 2013, $1.4 million of share-based compensation expense was capitalized to inventory and $2.0 million of previously capitalized share-based compensation expense in inventory was sold.

CONDENSED_CONSOLIDATED_STATEME2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Net income	$89,909	$78,579
Unrealized holding gain (losses), net of tax effect of $12 and $508, respectively	3,060	-10,098
Reclassification of realized transactions, net of tax effect of $12 and $0, respectively	-22	50
Other comprehensive income (loss), net of taxes	3,038	-10,048
Total comprehensive income	$92,947	$68,531

CONDENSED_CONSOLIDATED_STATEME3

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (PARENTHETICAL) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]	'	'
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$12	$508

CONDENSED_CONSOLIDATED_STATEME4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Cash flows from operating activities	'	'
Net income	$89,909	$78,579
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation and amortization	60,988	50,410
Deferred income taxes	-2,319	5,298
Share-based compensation expense related to equity incentive plans	13,321	12,656
Excess tax benefit from share-based compensation	0	0
Convertible debt derivatives - revaluation and amortization	-11	16
Amortization of debt discount on convertible debentures	2,365	2,161
Amortization of debt issuance costs	544	327
Losses on equity method investments	32	260
Impairment of intangible assets	406	0
Amortization of premium on available-for-sale investments	2,589	2,941
Special charge	0	1,392
Changes In Operating Assets And Liabilities	'	'
Increase in accounts receivable	-37,247	-2,462
Decrease (increase) in inventories	24,991	-13,957
(Decrease) increase in deferred income on shipments to distributors	-1,215	10,865
(Decrease) increase in accounts payable and accrued liabilities	-4,415	3,909
Change in other assets and liabilities	15,850	14,977
Net cash provided by operating activities	165,788	167,372
Cash flows from investing activities	'	'
Purchases of available-for-sale investments	-172,506	-379,401
Sales and maturities of available-for-sale investments	321,203	182,614
Acquisition of Supertex, net of cash acquired	-375,365	0
Other business acquisitions, net of cash acquired	0	-2,174
Investments in other assets	-1,123	-1,616
Proceeds from sale of assets	0	16,200
Capital expenditures	-44,637	-27,757
Net cash used in investing activities	-272,428	-212,134
Cash flows from financing activities:	'	'
Repayments of revolving loan under previous credit facility	0	-650,000
Repayments of revolving loan under new credit facility	-170,000	0
Proceeds from borrowings on revolving loan under previous credit facility	0	30,000
Proceeds from borrowings on revolving loan under new credit facility	504,375	260,000
Proceeds from issuance of long-term borrowings	0	350,000
Repayments of long-term borrowings	-4,375	0
Deferred financing costs	0	-7,515
Payment of cash dividends	-71,202	-69,682
Proceeds from sale of common stock	4,125	12,614
Tax payments related to shares withheld for vested restricted stock units	-4,968	-5,714
Capital lease payments	-148	-44
Excess tax benefit from share-based compensation	0	0
Net cash provided by (used in) financing activities	257,807	-80,341
Net increase (decrease) in cash and cash equivalents	151,167	-125,103
Cash and cash equivalents at beginning of period	466,603	528,334
Cash and cash equivalents at end of period	$617,770	$403,231

Basis_of_Presentation_Notes

Basis of Presentation (Notes)	3 Months Ended
	Jun. 30, 2014
Basis of Presentation [Abstract]	'
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]	'
	Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements include the accounts of Microchip Technology Incorporated and its wholly-owned subsidiaries (the Company).  All intercompany balances and transactions have been eliminated in consolidation.  The Company owns 100% of the outstanding stock in all of its subsidiaries.
	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America, pursuant to the rules and regulations of the Securities and Exchange Commission (the SEC).  The information furnished herein reflects all adjustments which are, in the opinion of management, of a normal recurring nature and necessary for a fair statement of the results for the interim periods reported. Certain information and footnote disclosures normally included in audited consolidated financial statements have been condensed or omitted pursuant to such SEC rules and regulations.  It is suggested that these condensed consolidated financial statements be read in conjunction with the audited consolidated financial statements and the notes thereto included in the Company's Annual Report on Form 10-K for the fiscal year ended March 31, 2014.  The results of operations for the three months ended June 30, 2014 are not necessarily indicative of the results that may be expected for the fiscal year ending March 31, 2015 or for any other period.
	As further discussed in Note 2, on April 1, 2014, the Company completed its acquisition of Supertex Incorporated (Supertex) and the Company's first quarter fiscal 2015 financial results include Supertex's results beginning as of the acquisition date.

Business_Acquisitions_Notes

Business Acquisitions (Notes)	3 Months Ended
	Jun. 30, 2014
Business Combinations [Abstract]	'
Business Acquisitions	'
	Business Acquisitions
	Acquisition of Supertex
	On April 1, 2014, the Company acquired Supertex, a publicly traded company based in Sunnyvale, California, for $33.00 per share and the exchange of certain share-based payment awards, for a total of $391.8 million. The Company financed the transaction using borrowings under its existing credit agreement. As a result of the acquisition, Supertex became a wholly owned subsidiary of the Company. Supertex is a leader in high voltage analog and mixed signal technologies, with a strong position in the medical, lighting and industrial control markets. The Company's primary reason for this acquisition was to expand the Company's range of solutions, products and capabilities in these areas by extending its served available market.
	The acquisition was accounted for under the acquisition method of accounting, with the Company identified as the acquirer, and the operating results of Supertex have been included in the Company's condensed consolidated financial statements as of the closing date of the acquisition. Under the acquisition method of accounting, the aggregate amount of consideration paid by the Company was allocated to Supertex's net tangible assets and intangible assets based on their estimated fair values as of April 1, 2014.  The excess of the purchase price over the value of the net tangible assets and intangible assets was recorded to goodwill. The goodwill has been allocated to the Company's semiconductor products reporting segment.  None of the goodwill related to the Supertex acquisition is deductible for tax purposes.  The Company retained an independent third-party appraiser to assist management in its valuation; however, the purchase price allocation has not been finalized. This could result in adjustments to the carrying value of the assets acquired and liabilities assumed, the useful lives of intangible assets and residual amount allocated to goodwill. The preliminary allocation of the purchase price is based on the best estimates of management and is subject to revision based on the final valuations and estimates of useful lives.
	The table below represents the preliminary allocation of the purchase price to the net assets acquired based on their estimated fair values as of April 1, 2014, as well as the associated estimated useful lives of the acquired intangible assets at that date (amounts in thousands):
	Assets acquired	1-Apr-14
	Cash and cash equivalents	$	14,790
	Short-term investments	140,984
	Accounts receivable, net	7,047
	Inventories	27,630
	Prepaid expenses	1,493
	Deferred tax assets	3,997
	Other current assets	16,113
	Property, plant and equipment, net	15,679
	Goodwill	133,713
	Purchased intangible assets	89,600
	Other assets	325
	Total assets acquired	451,371
	Liabilities assumed
	Accounts payable	(8,481		)
	Accrued liabilities	(19,345		)
	Long-term income tax payable	(3,796		)
	Deferred tax liability	(27,972		)
	Total liabilities assumed	(59,594		)
	Purchase price allocated	$	391,777
	The total purchase price allocated of $391.8 million includes approximately $1.6 million of non cash consideration for the exchange of certain share-based payment awards of Supertex for stock awards of the Company. The amount of cash paid by the Company, net of cash and short-term investments acquired from Supertex of approximately $155.8 million, was $234.4 million.
	Purchased Intangible Assets	Useful Life		1-Apr-14
		(in years)		(in thousands)
	Core/developed technology	10		$	68,900
	In-process technology	10		1,900
	Customer-related	2		17,700
	Backlog	1		1,100
				$	89,600
	Purchased intangible assets include core and developed technology, in-process research and development, customer-related intangibles and acquisition-date backlog. The estimated fair values of the core and developed technology and in-process research and development were determined based on the present value of the expected cash flows to be generated by the respective existing technology or future technology. The core and developed technology intangible assets are being amortized commensurate with the expected cash flows used in the initial determination of fair value. In-process technology is capitalized until such time the related projects are completed or abandoned at which time the capitalized amounts will begin to be amortized or written off.
	Customer-related intangible assets consist of Supertex's contractual relationships and customer loyalty related to its distributor and end-customer relationships, and the fair values of the customer-related intangibles were determined based on Supertex's projected revenues. An analysis of expected attrition and revenue growth for existing customers was prepared from Supertex's historical customer information.  Customer relationships are being amortized in a manner consistent with the estimated cash flows associated with the existing customers and anticipated retention rates. Backlog relates to the value of orders not yet shipped by Supertex at the acquisition date, and the preliminary fair values were based on the estimated profit associated with those orders. Backlog related assets are being recognized commensurate with recognition of the revenue for the orders on which the backlog intangible assets were determined.  Amortization expense associated with acquired intangible assets is not deductible for tax purposes.  Thus, approximately $22.8 million was established as a net deferred tax liability for the future amortization of the intangible assets.
	The amount of Supertex net sales and net loss included in the Company's condensed consolidated statements of income for the period April 1, 2014 to June 30, 2014 was $17.8 million and $17.7 million, respectively.
	The following unaudited pro-forma consolidated results of operations for the three months ended June 30, 2014 and 2013 assume the Supertex acquisition occurred as of April 1, 2013. The pro forma results of operations are presented for informational purposes only and are not indicative of the results of operations that would have been achieved if the acquisition had taken place on April 1, 2013 or of results that may occur in the future (amounts in thousands):
		Three Months Ended
		June 30,
		2014				2013
	Net sales	$	531,345			$	476,521
	Net income	105,505				60,964
	Basic earnings per share	$	0.53			$	0.31
	Diluted earnings per share	$	0.47			$	0.29

Recently_Issued_Accounting_Pro

Recently Issued Accounting Pronouncements (Notes)	3 Months Ended
	Jun. 30, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
Description of New Accounting Pronouncements Not yet Adopted [Text Block]	'
	Recently Issued Accounting Pronouncements
	In July 2013, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update No. 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (ASU 2013-11) to provide guidance on the presentation of unrecognized tax benefits. ASU 2013-11 requires an entity to present an unrecognized tax benefit, or a portion of an unrecognized tax benefit, as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward, except as follows: to the extent a net operating loss carryforward, a similar tax loss, or a tax credit carryforward is not available at the reporting date under the tax law of the applicable jurisdiction to settle any additional income taxes that would result from the disallowance of a tax position or the tax law of the applicable jurisdiction does not require the entity to use, and the entity does not intend to use, the deferred tax asset for such purpose, the unrecognized tax benefit should be presented in the financial statements as a liability and should not be combined with deferred tax assets. ASU 2013-11 is effective for the Company's first quarter of fiscal 2015 with earlier adoption permitted. ASU 2013-11 should be applied prospectively with retroactive application permitted. The Company evaluated the impact of adoption of ASU 2013-11 on its consolidated financial statements and determined that $51.9 million of unrecognized tax benefits can be presented as a reduction to deferred tax assets for net operating loss carryforward and other tax credit carryforwards. There was no income statement impact as a result of adopting this accounting standard.
	In May 2014, the FASB issued Accounting Standard Update 2014-09-Revenue from Contracts with Customers, which will supersede nearly all existing revenue recognition guidance under US GAAP.  The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The Company is carefully evaluating its existing revenue recognition policies to determine whether any contracts in the scope of the guidance will be materially affected by the new requirements.  The effects may include identifying performance obligations in existing arrangements, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation.  The new standard is effective beginning the first quarter of the Company’s 2018 fiscal year.  Early adoption is not permitted.  The standard allows for either "full retrospective" adoption, meaning the standard is applied to all of the periods presented, or "modified retrospective" adoption, meaning the standard is applied only to the most current period presented in the financial statements.  The Company is currently evaluating the transition method that will be elected.

Special_Charges_Notes

Special Charges (Notes)	3 Months Ended
	Jun. 30, 2014
Other Nonrecurring (Income) Expense [Abstract]	'
Special charges	'
	Special Charges
	The Company incurred special charges related to severance, office closing and other costs associated with its acquisition activity of $0.3 million and $1.7 million for the three months ended June 30, 2014 and June 30, 2013, respectively.

Segment_Information_Notes

Segment Information (Notes)	3 Months Ended
	Jun. 30, 2014
Segment Reporting [Abstract]	'
Segment Reporting Disclosure [Text Block]	'
	Segment Information
	The Company's reportable segments are semiconductor products and technology licensing.  The Company does not allocate operating expenses, interest income, interest expense, other income or expense, or provision for or benefit from income taxes to these segments for internal reporting purposes, as the Company does not believe that allocating these expenses is beneficial in evaluating segment performance.  Additionally, the Company does not allocate assets to segments for internal reporting purposes as it does not manage its segments by such metrics.
	The following table represents net sales and gross profit for each segment for the three months ended June 30, 2014 (amounts in thousands):
		Three Months Ended
		June 30, 2014
		Net Sales		Gross Profit
	Semiconductor products	$	508,439	$	286,082
	Technology licensing	20,437		20,437
		$	528,876	$	306,519
	The following table represents net sales and gross profit for each segment for the three months ended June 30, 2013 (amounts in thousands):
		Three Months Ended
		June 30, 2013
		Net Sales		Gross Profit
	Semiconductor products	$	440,274	$	244,056
	Technology licensing	22,518		22,518
		$	462,792	$	266,574

Investments_Notes

Investments (Notes)	3 Months Ended
	Jun. 30, 2014
Investments [Abstract]	'
Investments	'
	Investments
	The Company's investments are intended to establish a high-quality portfolio that preserves principal, meets liquidity needs, avoids inappropriate concentrations, and delivers an appropriate yield in relationship to the Company's investment guidelines and market conditions.  The following is a summary of available-for-sale securities at June 30, 2014 (amounts in thousands):
		Available-for-sale Securities
		Adjusted		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair Value
				Gains		Losses
	Government agency bonds	$	684,090	$	318	$	(1,108	)	$	683,300
	Municipal bonds	41,347		225		(7		)	41,565
	Auction rate securities	9,825		—		—			9,825
	Corporate bonds and debt	931,858		3,451		(369		)	934,940
		$	1,667,120	$	3,994	$	(1,484	)	$	1,669,630
	The following is a summary of available-for-sale securities at March 31, 2014 (amounts in thousands):
		Available-for-sale Securities
		Adjusted		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair Value
				Gains		Losses
	Government agency bonds	$	684,451	$	114	$	(3,171	)	$	681,394
	Municipal bonds	41,622		101		(14		)	41,709
	Auction rate securities	9,825		—		—			9,825
	Corporate bonds and debt	941,524		3,247		(805		)	943,966
		$	1,677,422	$	3,462	$	(3,990	)	$	1,676,894
	At June 30, 2014, the Company's available-for-sale debt securities are presented on the condensed consolidated balance sheets as short-term investments of $1,142.1 million and long-term investments of $527.5 million.  At March 31, 2014, the Company's available-for-sale debt securities are presented on the condensed consolidated balance sheets as short-term investments of $878.2 million and long-term investments of $798.7 million.
	At June 30, 2014, the Company evaluated its investment portfolio and noted unrealized losses of $1.5 million on its debt securities with an aggregated fair value of $519.6 million, which were due primarily to higher interest rates and resulting declines in market prices.  Management does not believe any of the unrealized losses represent an other-than-temporary impairment based on its evaluation of available evidence as of June 30, 2014 and the Company's intent is to hold these investments until these assets are no longer impaired, except for certain auction rate securities (ARS).  For those debt securities not scheduled to mature until after June 30, 2015, such recovery is not anticipated to occur in the next year and these investments have been classified as long-term investments.
	The amortized cost and estimated fair value of the available-for-sale securities at June 30, 2014, by contractual maturity, excluding corporate debt of $6.2 million, which has no contractual maturity, are shown below (amounts in thousands).  Expected maturities can differ from contractual maturities because the issuers of the securities may have the right to prepay obligations without prepayment penalties, and the Company views its available-for-sale securities as available for current operations.
		Adjusted		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair Value
				Gains		Losses
	Available-for-sale
	Due in one year or less	$	199,349	$	841	$	(6	)	$	200,184
	Due after one year and through five years	1,324,320		3,100		(762		)	1,326,658
	Due after five years and through ten years	127,436		53		(716		)	126,773
	Due after ten years	9,825		—		—			9,825
		$	1,660,930	$	3,994	$	(1,484	)	$	1,663,440
	The Company had no material realized gains or losses from the sale of available-for-sale marketable equity securities or debt securities during each of the three months ended June 30, 2014 and 2013.

Fair_Value_Measurements_Notes

Fair Value Measurements (Notes)	3 Months Ended
	Jun. 30, 2013
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements
	Accounting rules for fair value clarify that fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants.  As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability.  As a basis for considering such assumptions, the Company utilizes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:
	Level 1-	Observable inputs such as quoted prices in active markets;
	Level 2-	Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and
	Level 3-	Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.
	Marketable Debt Instruments
	Marketable debt instruments include instruments such as corporate bonds and debt, government agency bonds, bank deposits, municipal bonds, and money market fund deposits. When the Company uses observable market prices for identical securities that are traded in less active markets, the Company classifies its marketable debt instruments as Level 2. When observable market prices for identical securities are not available, the Company prices its marketable debt instruments using non-binding market consensus prices that are corroborated with observable market data; quoted market prices for similar instruments; or pricing models, such as a discounted cash flow model, with all significant inputs derived from or corroborated with observable market data. Non-binding market consensus prices are based on the proprietary valuation models of pricing providers or brokers. These valuation models incorporate a number of inputs, including non-binding and binding broker quotes; observable market prices for identical or similar securities; and the internal assumptions of pricing providers or brokers that use observable market inputs and, to a lesser degree, unobservable market inputs. The Company corroborates non-binding market consensus prices with observable market data using statistical models when observable market data exists. The discounted cash flow model uses observable market inputs, such as LIBOR-based yield curves, currency spot and forward rates, and credit ratings.
	Assets and Liabilities Measured at Fair Value on a Recurring Basis
	Assets measured at fair value on a recurring basis at June 30, 2014 are as follows (amounts in thousands):
		Quoted Prices				Significant			Significant				Total
		in Active				Other			Unobservable				Balance
		Markets for				Observable			Inputs
		Identical				Inputs			(Level 3)
		Instruments				(Level 2)
		(Level 1)
	Assets
	Money market mutual funds	$	8,051			$	—		$	—			$	8,051
	Corporate bonds and debt	—				928,750			6,190				934,940
	Government agency bonds	—				683,300			—				683,300
	Deposit accounts	—				609,719			—				609,719
	Municipal bonds	—				41,565			—				41,565
	Auction rate securities	—				—			9,825				9,825
	Total assets measured at fair value	$	8,051			$	2,263,334		$	16,015			$	2,287,400
	Assets measured at fair value on a recurring basis at March 31, 2014 are as follows (amounts in thousands):
		Quoted Prices				Significant			Significant				Total
		in Active				Other			Unobservable				Balance
		Markets for Identical Instruments				Observable			Inputs
		(Level 1)				Inputs			(Level 3)
						(Level 2)
	Assets
	Money market mutual funds	$	192,159			$	—		$	—			$	192,159
	Corporate bonds and debt	—				937,776			6,190				943,966
	Government agency bonds	—				681,394			—				681,394
	Deposit accounts	—				274,444			—				274,444
	Municipal bonds	—				41,709			—				41,709
	Auction rate securities	—				—			9,825				9,825
	Total assets measured at fair value	$	192,159			$	1,935,323		$	16,015			$	2,143,497
	There were no transfers between Level 1 and Level 2 during the three months ended June 30, 2014 or the year ended March 31, 2014.
	At June 30, 2014 and at March 31, 2014, the Company's ARS for which recent auctions were unsuccessful are made up of securities related to the insurance industry valued at $9.8 million with a par value of $22.4 million. The Company estimated the fair value of its ARS, which are classified as Level 3 securities, based on the following: (i) the underlying structure of each security; (ii) the present value of future principal and interest payments discounted at rates considered to reflect current market conditions; (iii) consideration of the probabilities of default, auction failure, or repurchase at par for each period; and (iv) estimates of the recovery rates in the event of default for each security. The significant unobservable inputs used in the fair value measurement of the insurance sector ARS as of June 30, 2014 were estimated risk free discount rates, liquidity risk premium, and the liquidity horizon. The risk free discount rate applied to these securities was 2% to 2.5% adjusted for the liquidity risk premium which ranged from 9.1% to 29.5%. The anticipated liquidity horizon ranged from 7 to 10 years. A significant increase in the liquidity premium or discount rate, in isolation, would lead to a significantly lower fair value measurement. A significant increase in the liquidity horizon, in isolation, would lead to a significantly lower fair value measurement. Each quarter the Company investigates material changes in the fair value measurements of its ARS.
	The following tables present a reconciliation for all assets and liabilities measured at fair value on a recurring basis, excluding accrued interest components, using significant unobservable inputs (Level 3) for the year ended March 31, 2014 (amounts in thousands):
	Year ended March 31, 2014		Auction Rate				Corporate			Contingent				Total Gains
			Securities				Debt			Consideration				(Losses)
	Balance at March 31, 2013		$	33,791			$	6,190		$	(19,100	)		$	—
	Total gains (losses) (realized and unrealized):
	Included in earnings		1,101				—			(1,370		)		(269		)
	Included in other comprehensive income		(332		)		—			—				(332		)
	Purchases, sales, issuances, and settlements, net		(24,735		)		—			20,470				—
	Balance at March 31, 2014		$	9,825			$	6,190		$	—			$	(601	)
	Gains and losses recognized in earnings using Level 3 inputs for ARS are credited or charged to Other Income (Expense) on the condensed consolidated statements of income. Gains and losses recognized in earnings using Level 3 inputs related to the revaluation of contingent consideration are credited or charged to Special Charges on the condensed consolidated statements of income.
	Assets measured at fair value on a recurring basis are presented/classified on the condensed consolidated balance sheets at June 30, 2014 as follows (amounts in thousands):
		Quoted Prices				Significant			Significant				Total
		in Active				Other			Unobservable				Balance
		Markets for				Observable			Inputs
		Identical				Inputs			(Level 3)
		Instruments				(Level 2)
		(Level 1)
	Assets
	Cash and cash equivalents	$	8,051			$	609,719		$	—			$	617,770
	Short-term investments	—				1,142,091			—				1,142,091
	Long-term investments	—				511,524			16,015				527,539
	Total assets measured at fair value	$	8,051			$	2,263,334		$	16,015			$	2,287,400
	Assets measured at fair value on a recurring basis are presented/classified in the condensed consolidated balance sheets at March 31, 2014 as follows (amounts in thousands):
		Quoted Prices				Significant			Significant				Total
in Active			Other			Unobservable			Balance
Markets for			Observable			Inputs
Identical			Inputs			(Level 3)
Instruments			(Level 2)
(Level 1)
Assets
Cash and cash equivalents	$	192,159			$	274,444		$	—			$	466,603
Short-term investments	—				878,182			—				878,182
Long-term investments	—				782,697			16,015				798,712
Total assets measured at fair value	$	192,159			$	1,935,323		$	16,015			$	2,143,497
Financial Assets Not Recorded at Fair Value on a Recurring Basis
The Company's non-marketable equity and cost-method investments are not recorded at fair value on a recurring basis.  These investments are monitored on a quarterly basis for impairment charges.  The investments will only be recorded at fair value when an impairment charge is recognized.  There were no impairment charges recognized on these investments in the three months ended June 30, 2014 and June 30, 2013.

Fair_Value_of_Financial_Instru

Fair Value of Financial Instruments (Notes)	3 Months Ended
	Jun. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value of Financial Instruments	'
	Fair Value of Financial Instruments
	The carrying amount of cash equivalents approximates fair value because their maturity is less than three months.  Management believes the carrying amount of the equity and cost-method investments materially approximated fair value at June 30, 2014 based upon unobservable inputs. The fair values of these investments have been determined as Level 3 fair value measurements. The fair values of the Company's line of credit and short-term and long-term borrowings are estimated using discounted cash flow analyses, based on the Company's current incremental borrowing rates for similar types of borrowing arrangements and approximate carrying value. Based on the borrowing rates currently available to the Company for bank loans with similar terms and average maturities, the fair value of the Company's line of credit and long-term borrowings at June 30, 2014 approximated book value and are considered Level 2 in the fair value hierarchy described in Note 7. The carrying amount of accounts receivable, accounts payable and accrued liabilities approximates fair value due to the short-term maturity of the amounts.  The fair value of the Company's junior subordinated convertible debentures was $2.197 billion at June 30, 2014 and $2.138 billion at March 31, 2014 based on observable market prices for these debentures, which are traded in less active markets and are therefore classified as Level 2 securities.

Accounts_Receivable_Notes

Accounts Receivable (Notes)	3 Months Ended
	Jun. 30, 2014
Accounts Receivable, Net [Abstract]	'
Accounts Receivable	'
	Accounts Receivable
	Accounts receivable consists of the following (amounts in thousands):
		June 30, 2014		March 31, 2014
	Trade accounts receivable	$	287,415	$	243,383
	Other	2,300		1,940
		289,715		245,323
	Less allowance for doubtful accounts	3,016		2,918
		$	286,699	$	242,405

Inventories_Notes

Inventories (Notes)	3 Months Ended
	Jun. 30, 2014
Inventory Disclosure [Abstract]	'
Inventories	'
	Inventories
	The components of inventories consist of the following (amounts in thousands):
		June 30, 2014		March 31, 2014
	Raw materials	$	11,154	$	9,734
	Work in process	189,419		179,692
	Finished goods	63,932		73,299
		$	264,505	$	262,725
	Inventories are valued at the lower of cost or market using the first-in, first-out method. Inventory impairment charges establish a new cost basis for inventory and charges are not subsequently reversed to income even if circumstances later suggest that increased carrying amounts are recoverable.

Property_Plant_and_Equipment_N

Property, Plant and Equipment (Notes)	3 Months Ended
	Jun. 30, 2014
Property, Plant and Equipment [Abstract]	'
Property, Plant and Equipment Disclosure [Text Block]	'
	Property, Plant and Equipment
	Property, plant and equipment consists of the following (amounts in thousands):
		June 30, 2014		March 31, 2014
	Land	$	70,720	$	55,624
	Building and building improvements	414,826		411,149
	Machinery and equipment	1,495,018		1,465,255
	Projects in process	81,109		68,991
		2,061,673		2,001,019
	Less accumulated depreciation and amortization	1,491,765		1,469,052
		$	569,908	$	531,967
	Depreciation expense attributed to property, plant and equipment was $23.3 million for the three months ended June 30, 2014 and $21.4 million for the three months ended June 30, 2013.

Intangible_Assets_and_Goodwill

Intangible Assets and Goodwill (Notes)	3 Months Ended
	Jun. 30, 2014
Goodwill and Intangible Assets Disclosure [Abstract]	'
Intangible Assets and Goodwill	'
	Intangible Assets and Goodwill
	Intangible assets consist of the following (amounts in thousands):
			June 30, 2014
			Gross Amount			Accumulated Amortization			Net Amount
	Developed technology		$	493,248		$	(137,650	)	$	355,598
	Customer-related		213,500			(125,580		)	87,920
	Trademarks and trade names		15,730			(7,721		)	8,009
	Backlog		25,710			(24,885		)	825
	In-process technology		45,335			—			45,335
	Distribution rights		5,585			(5,193		)	392
	Covenants not to compete		400			(400		)	—
			$	799,508		$	(301,429	)	$	498,079
			March 31, 2014
			Gross Amount			Accumulated Amortization			Net Amount
	Developed technology		$	402,669		$	(117,222	)	$	285,447
	Customer-related		195,800			(109,170		)	86,630
	Trademarks and trade names		15,730			(7,118		)	8,612
	Backlog		24,610			(24,610		)	—
	In-process technology		64,396			—			64,396
	Distribution rights		5,585			(5,171		)	414
	Covenants not to compete		400			(400		)	—
			$	709,190		$	(263,691	)	$	445,499
	The Company amortizes intangible assets over their expected useful lives, which range between 1 and 15 years.  In the three months ended June 30, 2014, as a result of the Supertex acquisition, the Company acquired $68.9 million of developed technology which has an amortization period of 10 years, $17.7 million of customer-related intangible assets which has an amortization period of 2 years, $1.1 million of intangible assets related to acquisition date backlog which has an amortization period of approximately 1 year and $1.9 million of in-process technology which will begin amortization once the technology reaches technological feasibility. During the three months ended June 30, 2014, $21.2 million of in-process technology reached technological feasibility and was reclassified as developed technology and began being amortized over its estimated useful life. The following is an expected amortization schedule for the intangible assets for the remainder of fiscal 2015 through fiscal 2019, absent any future acquisitions or impairment charges (amounts in thousands):
	Year ending	Projected Amortization
	March 31,	Expense
	2015	$114,073
	2016	107,173
	2017	71,652
	2018	57,187
	2019	48,964
	Amortization expense attributed to intangible assets was $37.7 million and $28.9 million for the three months ended June 30, 2014 and June 30, 2013, respectively.  In the three months ended June 30, 2014, approximately $1.0 million was charged to cost of sales and approximately $36.7 million was charged to operating expenses.  In the three months ended June 30, 2013, approximately $1.3 million was charged to cost of sales and approximately $27.6 million was charged to operating expenses.  The Company recognized impairment charges of $0.4 million in the three months ended June 30, 2014. The Company found no indication of impairment of its intangible assets in the three months ended June 30, 2013.
	Goodwill activity for the three months ended June 30, 2014 was as follows (amounts in thousands):
		Semiconductor Products			Technology
		Reporting Unit			Licensing
					Reporting Unit
	Balance at March 31, 2014	$	256,897		$	19,200
	Additions due to the acquisition of Supertex	133,713			—
	Adjustments due to other acquisitions	75			—
	Balance at June 30, 2014	$	390,685		$	19,200
	In the three months ended June 30, 2014, the Company completed its acquisition of Supertex which resulted in goodwill of approximately $133.7 million which was allocated to the semiconductor products reporting unit.
	At June 30, 2014, $390.7 million of goodwill was recorded in the Company's semiconductor products reporting unit and $19.2 million was recorded in the Company's technology licensing reporting unit. At March 31, 2014, the Company applied a qualitative goodwill impairment screen to its two reporting units, concluding it was not more likely than not that goodwill was impaired. Through June 30, 2014, the Company had never recorded an impairment charge against its goodwill balance.

Income_taxes_Notes

Income taxes (Notes)	3 Months Ended
	Jun. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes
	The provision for income taxes reflects tax on foreign earnings and federal and state tax on U.S. earnings.  The Company had an effective tax rate of 16.0% for the three-month period ended June 30, 2014 and 13.0% for the three-month period ended June 30, 2013.  The Company's effective tax rate is lower than statutory rates in the U.S. due primarily to its mix of earnings in foreign jurisdictions with lower tax rates. The Company's effective tax rate was higher in the June 30, 2014 period due to certain tax expenses associated with its acquisition of Supertex.
	At June 30, 2014, the Company had $196.4 million of unrecognized tax benefits.  Unrecognized tax benefits increased by $16.4 million compared to March 31, 2014 primarily as a result of unrecognized tax benefits from the acquisition of Supertex, the ongoing accrual for uncertain tax positions and the accrual of deficiency interest on these positions. The Company evaluated the impact of the adoption of ASU 2013-11 on its condensed consolidated financial statements and determined that $51.9 million of unrecognized tax benefits can be presented as a reduction to deferred tax assets for net operating loss carryforward and other tax credit carryforwards. There was no income statement impact as a result of adopting this accounting standard.
	The Company files U.S. federal, U.S. state, and foreign income tax returns.  For U.S. federal, and in general for U.S. state tax returns, the fiscal 2011 and later tax years remain open for examination by tax authorities.  The U.S. Internal Revenue Service (IRS) is currently auditing Microchip's and SMSC's 2011 and 2012 tax years.  The IRS is also currently auditing Supertex's 2011, 2012 and 2013 tax years. For foreign tax returns, the Company is generally no longer subject to income tax examinations for years prior to fiscal 2006.
	The Company recognizes liabilities for anticipated tax audit issues in the U.S. and other domestic and international tax jurisdictions based on its estimate of whether, and the extent to which, additional tax payments are more likely than not.  The Company believes that it has appropriate support for the income tax positions taken and to be taken on its tax returns and that its accruals for tax liabilities are adequate for all open years based on an assessment of many factors including past experience and interpretations of tax laws applied to the facts of each matter.
	The Company believes it maintains appropriate reserves to offset any potential income tax liabilities that may arise upon final resolution of matters for open tax years.  If such reserve amounts ultimately prove to be unnecessary, the resulting reversal of such reserves would result in tax benefits being recorded in the period the reserves are no longer deemed necessary.  If such amounts prove to be less than an ultimate assessment, a future charge to expense would be recorded in the period in which the assessment is determined.  Although the timing of the resolution and/or closure of audits is highly uncertain, the Company does not believe it is reasonably possible that the unrecognized tax benefits would materially change in the next 12 months.

2125_Junior_subordinated_conve

2.125% Junior subordinated convertible debentures (Notes)	3 Months Ended
	Jun. 30, 2014
Convertible Debt [Abstract]	'
Junior subordinated convertible debentures	'
	2.125% Junior Subordinated Convertible Debentures
	The Company's $1.15 billion principal amount of 2.125% junior subordinated convertible debentures due December 15, 2037, are subordinated in right of payment to any future senior debt of the Company and are effectively subordinated in right of payment to the liabilities of the Company's subsidiaries.  The debentures are convertible, subject to certain conditions, into shares of the Company's common stock at an initial conversion rate of 29.2783 shares of common stock per $1,000 principal amount of debentures, representing an initial conversion price of approximately $34.16 per share of common stock.  As of June 30, 2014, the holders of the debentures have the right to convert their debentures between July 1, 2014 and September 30, 2014 because for at least 20 trading days during the 30 consecutive trading day period ending on June 30, 2014, the Company's common stock had a last reported sale price greater than 130% of the conversion price. As of June 30, 2014, a holder could realize more economic value by selling its debentures in the over the counter market than from converting its debentures. As a result of cash dividends paid since the issuance of the debentures, the conversion rate has been adjusted to 38.9573 shares of common stock per $1,000 of principal amount of debentures, representing a conversion price of approximately $25.67 per share of common stock. The debentures include a contingent interest mechanism that begins in December 2017. The terms of the contingent interest include a 0.25% interest rate if the debentures are trading at less than $40 and 0.5% if the debentures are trading at greater than $150. Based on the current trading price of the debentures, the contingent interest rate in calendar year 2017 would be 0.5%.
	As the debentures can be settled in cash upon conversion, for accounting purposes, the debentures were bifurcated into a liability component and an equity component, which are both initially recorded at fair value.  The carrying value of the equity component at June 30, 2014 and at March 31, 2014 was $822.4 million.  The estimated fair value of the liability component of the debentures at the issuance date was $327.6 million, resulting in a debt discount of $822.4 million.  The unamortized debt discount was $774.9 million at June 30, 2014 and $777.2 million at March 31, 2014.  The carrying value of the debentures was $374.2 million at June 30, 2014 and $371.9 million at March 31, 2014.  The remaining period over which the unamortized debt discount will be recognized as non-cash interest expense is 23.5 years.  In the three months ended June 30, 2014, the Company recognized $2.4 million in non-cash interest expense related to the amortization of the debt discount.  In the three months ended June 30, 2013, the Company recognized $2.2 million in non-cash interest expense related to the amortization of the debt discount.  The Company recognized $6.1 million of interest expense related to the 2.125% coupon on the debentures in each of the three-month periods ended June 30, 2014 and June 30, 2013.

Credit_facility_Notes

Credit facility (Notes)	3 Months Ended
	Jun. 30, 2014
Line of Credit Facility [Abstract]	'
Credit Facility	'
	Credit Facility
	On June 27, 2013, the Company entered into a $2.0 billion credit agreement among the Company, the lenders from time to time that are parties thereto and JPMorgan Chase Bank, N.A., as administrative agent (the Credit Agreement). The Credit Agreement provides for a $350 million term loan and a $1.65 billion revolving credit facility, with a $125 million foreign currency sublimit, a $35 million letter of credit sublimit and a $25 million swingline loan sublimit, terminating on June 27, 2018 (the Maturity Date). The Credit Agreement also contains an increase option permitting the Company, subject to certain requirements, to arrange with existing lenders and/or new lenders for them to provide up to an aggregate of $300 million in additional commitments, which may be for revolving loans or term loans. Proceeds of loans made under the Credit Agreement may be used for working capital and general corporate purposes. The Credit Agreement replaced another credit agreement the Company had in place since August 2011. At June 30, 2014, $980.0 million of borrowings were outstanding under the Credit Agreement consisting of $634.4 million of a revolving line of credit and $345.6 million of a term loan, net of $1.0 million of debt discount resulting from amounts paid to the lenders.
	The loans under the Credit Agreement bear interest, at the Company's option, at the base rate plus a spread of 0.25% to 1.25% or an adjusted LIBOR rate (based on one, two, three, or six-month interest periods) plus a spread of 1.25% to 2.25%, in each case with such spread being determined based on the consolidated leverage ratio for the preceding four fiscal quarter period. The base rate means the highest of JPMorgan Chase Bank, N.A.'s prime rate, the federal funds rate plus a margin equal to 0.50% and the adjusted LIBOR rate for a 1-month interest period plus a margin equal to 1.00%. Swingline loans accrue interest at a per annum rate based on the base rate plus the applicable margin for base rate loans. Base rate loans may only be made in U.S. dollars. The Company is also obligated to pay other customary administration fees and letter of credit fees for a credit facility of this size and type.
	Interest is due and payable in arrears quarterly for loans bearing interest at the base rate and at the end of an interest period (or at each three-month interval in the case of loans with interest periods greater than three months) in the case of loans bearing interest at the adjusted LIBOR rate. Interest expense related to the Credit Agreement was approximately $5.0 million in the three months ended June 30, 2014 and $3.4 million in the three months ended June 30, 2013. Principal, together with all accrued and unpaid interest, is due and payable on the Maturity Date. The weighted average interest rate on short-term borrowings outstanding at June 30, 2014 related to the Credit Agreement was 1.65%. The Company also pays a quarterly commitment fee on the available but unused portion of its line of credit which is calculated on the average daily available balance during the period. The Company may prepay the loans and terminate the commitments, in whole or in part, at any time without premium or penalty, subject to certain conditions including minimum amounts in the case of commitment reductions and reimbursement of certain costs in the case of prepayments of LIBOR loans.
	The Company's obligations under the Credit Agreement are guaranteed by certain of its subsidiaries meeting materiality thresholds set forth in the Credit Agreement. To secure the Company's obligations under the Credit Agreement, the Company and its domestic subsidiaries will be required to pledge the equity securities of certain of their respective material subsidiaries, subject to certain exceptions and limitations.
	The Credit Agreement contains customary affirmative and negative covenants, including covenants that limit or restrict the Company and its subsidiaries' ability to, among other things, incur subsidiary indebtedness, grant liens, merge or consolidate, dispose of assets, make investments, make acquisitions, enter into certain transactions with affiliates, pay dividends or make distributions, repurchase stock, enter into restrictive agreements and enter into sale and leaseback transactions, in each case subject to customary exceptions for a credit facility of this size and type. The Company is also required to maintain compliance with a consolidated leverage ratio and a consolidated interest coverage ratio. At June 30, 2014, the Company was in compliance with these covenants.
	The Credit Agreement includes customary events of default that include, among other things, non-payment defaults, inaccuracy of representations and warranties, covenant defaults, cross default to material indebtedness, bankruptcy and insolvency defaults, material judgment defaults, ERISA defaults and a change of control default. The occurrence of an event of default could result in the acceleration of the obligations under the Credit Agreement. Under certain circumstances, a default interest rate will apply on all obligations during the existence of an event of default under the Credit Agreement at a per annum rate equal to 2.00% above the applicable interest rate for any overdue principal and 2.00% above the rate applicable for base rate loans for any other overdue amounts.

Contingencies_Notes

Contingencies (Notes)	3 Months Ended
	Jun. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Contingencies	'
	Contingencies
	In the ordinary course of the Company's business, it is involved in a limited number of legal actions, both as plaintiff and defendant, and could incur uninsured liability in any one or more of them.  The Company also periodically receives notifications from various third parties alleging infringement of patents, intellectual property rights or other matters.  With respect to pending legal actions to which the Company is a party, although the outcomes of these actions are not generally determinable, the Company believes that the ultimate resolution of these matters will not have a material adverse effect on its financial position, cash flows or results of operations.  Litigation relating to the semiconductor industry is not uncommon, and the Company is, and from time to time has been, subject to such litigation.  No assurances can be given with respect to the extent or outcome of any such litigation in the future.
	The Company's technology license agreements generally include an indemnification clause that indemnifies the licensee against liability and damages (including legal defense costs) arising from any claims of patent, copyright, trademark or trade secret infringement by the Company's proprietary technology.  The terms of these indemnification provisions approximate the terms of the outgoing technology license agreements, which are typically perpetual unless terminated by either party for breach.  The possible amount of future payments the Company could be required to make based on agreements that specify indemnification limits, if such indemnifications were required on all of these agreements, is approximately $132 million. There are some licensing agreements in place that do not specify indemnification limits.  The Company had not recorded any liabilities related to these indemnification obligations as of June 30, 2014.
	At June 30, 2014, the Company had recognized a contingent liability in the amount of $5.7 million recorded in connection with the Company's April 8, 2010 acquisition of Silicon Storage Technology Inc. (SST) as an adverse outcome was determined to be probable and estimable.

Derivative_Instruments_Notes

Derivative Instruments (Notes)	3 Months Ended
	Jun. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Instruments and Hedging Activities Disclosure [Text Block]	'
	Derivative Instruments
	The Company has international operations and is thus subject to foreign currency rate fluctuations.  To help manage the risk of changes in foreign currency rates, the Company periodically enters into derivative contracts comprised of foreign currency forward contracts to hedge its asset and liability foreign currency exposure and a portion of its foreign currency operating expenses.  Approximately 99% of the Company's sales are U.S. dollar denominated.  To date, the exposure related to foreign exchange rate volatility has not been material to the Company's operating results.  As of June 30, 2014 and March 31, 2014, the Company had no foreign currency forward contracts outstanding. The Company recognized an immaterial amount of net realized gains and losses on foreign currency forward contracts in each of the three months ended June 30, 2014 and 2013. Gains and losses from changes in the fair value of these foreign currency forward contracts are credited or charged to Other Income (Expense). The Company does not apply hedge accounting to its foreign currency derivative instruments.

Comprehensive_Income_Notes

Comprehensive Income (Notes)	3 Months Ended
	Jun. 30, 2014
Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Comprehensive Income	'
	Comprehensive Income
	The following table presents the changes in the components of accumulated other comprehensive income (AOCI) for the three months ended June 30, 2014 (amounts in thousands):
		Unrealized				Minimum			Foreign		Total
		holding gains (losses)				pension			Currency
		available-for-sale securities				liability
	Balance at March 31, 2014	$	(528	)		$	140		$	1,439	$	1,051
	Other comprehensive income before reclassifications	3,060				—			—		3,060
	Amounts reclassified from accumulated other comprehensive income (loss)	(22		)		—			—		(22		)
	Net other comprehensive income	3,038				—			—		3,038
	Balance at June 30, 2014	$	2,510			$	140		$	1,439	$	4,089
	The table below details where reclassifications of realized transactions out of AOCI are recorded on the Condensed Consolidated Statements of Income (amounts in thousands):
			Three Months Ended
			June 30,
	Description of AOCI Component		2014				2013			Related Statement
										of Income Line
	Unrealized gains on available-for-sale securities		$	34			$	50		Other income
	Taxes		(12		)		—			Provision for income taxes
	Reclassification of realized transactions, net of taxes		$	22			$	50		Net income

ShareBased_Compensation_Notes

Share-Based Compensation (Notes)	3 Months Ended
	Jun. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Equity incentive plans	'
	Share-Based Compensation
	The following table presents the details of the Company's share-based compensation expense (amounts in thousands):
		Three Months Ended
		June 30,
		2014			2013
	Cost of sales	$	2,055	(1)	$	1,969	(1)
	Research and development	6,309			5,690
	Selling, general and administrative	4,957			4,997
	Pre-tax effect of share-based compensation	13,321			12,656
	Income tax benefit	1,420			1,402
	Net income effect of share-based compensation	$	11,901		$	11,254
	(1) During the three months ended June 30, 2014, $1.7 million of share-based compensation expense was capitalized to inventory and $2.1 million of previously capitalized share-based compensation expenses in inventory was sold.  During the three months ended June 30, 2013, $1.4 million of share-based compensation expense was capitalized to inventory and $2.0 million of previously capitalized share-based compensation expense in inventory was sold.

Net_income_per_common_share_No

Net income per common share (Notes)	3 Months Ended
	Jun. 30, 2014
Earnings Per Share [Abstract]	'
Net income per common share	'
	Net Income Per Common Share
	The following table sets forth the computation of basic and diluted net income per common share (in thousands, except per share amounts):
		Three Months Ended
		June 30,
		2014		2013
	Net income	$	89,909	$	78,579
	Weighted average common shares outstanding	200,187		196,950
	Dilutive effect of stock options and RSUs	3,792		3,672
	Dilutive effect of convertible debt	20,548		11,644
	Weighted average common and potential common shares outstanding	224,527		212,266
	Basic net income per common share	$	0.45	$	0.4
	Diluted net income per common share	$	0.4	$	0.37
	We computed basic earnings per common share using net income available to common stockholders and the weighted average number of common shares outstanding during the period. We computed diluted earnings per common share using net income available to common stockholders and the weighted average number of common shares outstanding plus potentially dilutive common shares outstanding during the period.
	Potentially dilutive common shares from employee equity incentive plans are determined by applying the treasury stock method to the assumed exercise of outstanding stock options and the assumed vesting of outstanding RSUs.
	Diluted net income per common share for the three months ended June 30, 2014 includes 20,547,832 shares issuable upon the exchange of debentures (see Note 14).  Diluted net income per common share for the three months ended June 30, 2013 includes 11,644,236 issuable upon the exchange of debentures.  The debentures have no impact on diluted net income per common share unless the average price of the Company's common stock exceeds the conversion price because the principal amount of the debentures will be settled in cash upon conversion.  Prior to conversion, the Company will include, in the diluted net income per common share calculation, the effect of the additional shares that may be issued when the Company's common stock price exceeds the conversion price using the treasury stock method.  The weighted average conversion price per share used in calculating the dilutive effect of the convertible debt for the three-month periods ended June 30, 2014 and June 30, 2013 was $25.75 and $26.66, respectively.
	Weighted average common shares exclude the effect of option shares which are not dilutive.  There were no antidilutive option shares for the three months ended June 30, 2014. For the three months ended June 30, 2013, the number of option shares that were antidilutive was 50,198.

Dividends_Notes

Dividends (Notes)	3 Months Ended
	Jun. 30, 2014
Dividends [Abstract]	'
Dividends [Text Block]	'
	Dividends
	A quarterly cash dividend of $0.3555 per share was paid on June 3, 2014 in the aggregate amount of $71.2 million.  A quarterly cash dividend of $0.356 per share was declared on July 31, 2014 and will be paid on September 4, 2014 to stockholders of record as of August 21, 2014. The Company expects the September 2014 payment of its quarterly cash dividend to be approximately $71.4 million.

Subsequent_Event_Notes

Subsequent Event (Notes)	3 Months Ended
	Jun. 30, 2014
Subsequent Events [Abstract]	'
Subsequent Event	'
	Subsequent Event
	Announcement of Completion of ISSC Technologies Tender Offer
	On July 14, 2014, the Company announced the successful completion of the tender offer to acquire the outstanding shares of Taiwan based ISSC Technologies Corporation (ISSC). As of the expiration date of the tender offer on July 14, 2014, a total of 57,228,225 shares were tendered, representing approximately 83.46% of the outstanding shares of ISSC, exceeding the minimum tender condition of 27,300,429 shares. The shares were tendered at the offer price of New Taiwan Dollar (NT$) 143 per share (approximately US$4.74 per share). As a result of the completion of the tender offer, through its indirect wholly owned Cayman Island subsidiary, the Company owns the majority of the outstanding shares of ISSC and will consolidate ISSC's financial statements in the quarter ended September 30, 2014. ISSC is a leading provider of low power Bluetooth and advanced wireless solutions for the Internet Of Things (IoT) market. Under the terms of the transaction, the Company will acquire the remaining shares of ISSC pursuant to a follow-on merger at approximately $4.74 per share minus any dividends paid by ISSC prior to the close of the transaction. The transaction represents a total equity value of approximately $328.5 million (approximately NT$9.9 billion), and a total enterprise value of about $287.1 million (approximately NT$8.7 billion), after excluding ISSC's cash and investments on its balance sheet of approximately $41.4 million (approximately NT$1.2 billion).

Business_Acquisitions_Tables

Business Acquisitions (Tables)	3 Months Ended
	Jun. 30, 2014
Business Combinations [Abstract]	'
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	'
	The table below represents the preliminary allocation of the purchase price to the net assets acquired based on their estimated fair values as of April 1, 2014, as well as the associated estimated useful lives of the acquired intangible assets at that date (amounts in thousands):
	Assets acquired	1-Apr-14
	Cash and cash equivalents	$	14,790
	Short-term investments	140,984
	Accounts receivable, net	7,047
	Inventories	27,630
	Prepaid expenses	1,493
	Deferred tax assets	3,997
	Other current assets	16,113
	Property, plant and equipment, net	15,679
	Goodwill	133,713
	Purchased intangible assets	89,600
	Other assets	325
	Total assets acquired	451,371
	Liabilities assumed
	Accounts payable	(8,481		)
	Accrued liabilities	(19,345		)
	Long-term income tax payable	(3,796		)
	Deferred tax liability	(27,972		)
	Total liabilities assumed	(59,594		)
	Purchase price allocated	$	391,777
Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination	'
	Purchased Intangible Assets	Useful Life		1-Apr-14
		(in years)		(in thousands)
	Core/developed technology	10		$	68,900
	In-process technology	10		1,900
	Customer-related	2		17,700
	Backlog	1		1,100
				$	89,600
Business Acquisition, Pro Forma Information	'
	The following unaudited pro-forma consolidated results of operations for the three months ended June 30, 2014 and 2013 assume the Supertex acquisition occurred as of April 1, 2013. The pro forma results of operations are presented for informational purposes only and are not indicative of the results of operations that would have been achieved if the acquisition had taken place on April 1, 2013 or of results that may occur in the future (amounts in thousands):
		Three Months Ended
		June 30,
		2014				2013
	Net sales	$	531,345			$	476,521
	Net income	105,505				60,964
	Basic earnings per share	$	0.53			$	0.31
	Diluted earnings per share	$	0.47			$	0.29

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Jun. 30, 2014
Segment Reporting [Abstract]	'
Revenues and gross profit for each segment	'
	The following table represents net sales and gross profit for each segment for the three months ended June 30, 2014 (amounts in thousands):
		Three Months Ended
		June 30, 2014
		Net Sales		Gross Profit
	Semiconductor products	$	508,439	$	286,082
	Technology licensing	20,437		20,437
		$	528,876	$	306,519
	The following table represents net sales and gross profit for each segment for the three months ended June 30, 2013 (amounts in thousands):
		Three Months Ended
		June 30, 2013
		Net Sales		Gross Profit
	Semiconductor products	$	440,274	$	244,056
	Technology licensing	22,518		22,518
		$	462,792	$	266,574

Investments_Tables

Investments (Tables)	3 Months Ended
	Jun. 30, 2014
Investments [Abstract]	'
Summary of available-for-sale securities	'
	The following is a summary of available-for-sale securities at June 30, 2014 (amounts in thousands):
		Available-for-sale Securities
		Adjusted		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair Value
				Gains		Losses
	Government agency bonds	$	684,090	$	318	$	(1,108	)	$	683,300
	Municipal bonds	41,347		225		(7		)	41,565
	Auction rate securities	9,825		—		—			9,825
	Corporate bonds and debt	931,858		3,451		(369		)	934,940
		$	1,667,120	$	3,994	$	(1,484	)	$	1,669,630
	The following is a summary of available-for-sale securities at March 31, 2014 (amounts in thousands):
		Available-for-sale Securities
		Adjusted		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair Value
				Gains		Losses
	Government agency bonds	$	684,451	$	114	$	(3,171	)	$	681,394
	Municipal bonds	41,622		101		(14		)	41,709
	Auction rate securities	9,825		—		—			9,825
	Corporate bonds and debt	941,524		3,247		(805		)	943,966
		$	1,677,422	$	3,462	$	(3,990	)	$	1,676,894
Summary of amortized cost and estimated fair value of available-for-sale securities, by maturity	'
	The amortized cost and estimated fair value of the available-for-sale securities at June 30, 2014, by contractual maturity, excluding corporate debt of $6.2 million, which has no contractual maturity, are shown below (amounts in thousands).  Expected maturities can differ from contractual maturities because the issuers of the securities may have the right to prepay obligations without prepayment penalties, and the Company views its available-for-sale securities as available for current operations.
		Adjusted		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair Value
				Gains		Losses
	Available-for-sale
	Due in one year or less	$	199,349	$	841	$	(6	)	$	200,184
	Due after one year and through five years	1,324,320		3,100		(762		)	1,326,658
	Due after five years and through ten years	127,436		53		(716		)	126,773
	Due after ten years	9,825		—		—			9,825
		$	1,660,930	$	3,994	$	(1,484	)	$	1,663,440

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Jun. 30, 2014
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]	'
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	'
	Assets measured at fair value on a recurring basis at June 30, 2014 are as follows (amounts in thousands):
		Quoted Prices				Significant			Significant				Total
		in Active				Other			Unobservable				Balance
		Markets for				Observable			Inputs
		Identical				Inputs			(Level 3)
		Instruments				(Level 2)
		(Level 1)
	Assets
	Money market mutual funds	$	8,051			$	—		$	—			$	8,051
	Corporate bonds and debt	—				928,750			6,190				934,940
	Government agency bonds	—				683,300			—				683,300
	Deposit accounts	—				609,719			—				609,719
	Municipal bonds	—				41,565			—				41,565
	Auction rate securities	—				—			9,825				9,825
	Total assets measured at fair value	$	8,051			$	2,263,334		$	16,015			$	2,287,400
	Assets measured at fair value on a recurring basis at March 31, 2014 are as follows (amounts in thousands):
		Quoted Prices				Significant			Significant				Total
		in Active				Other			Unobservable				Balance
		Markets for Identical Instruments				Observable			Inputs
		(Level 1)				Inputs			(Level 3)
						(Level 2)
	Assets
	Money market mutual funds	$	192,159			$	—		$	—			$	192,159
	Corporate bonds and debt	—				937,776			6,190				943,966
	Government agency bonds	—				681,394			—				681,394
	Deposit accounts	—				274,444			—				274,444
	Municipal bonds	—				41,709			—				41,709
	Auction rate securities	—				—			9,825				9,825
	Total assets measured at fair value	$	192,159			$	1,935,323		$	16,015			$	2,143,497
Reconciliation of assets and liabilities measured at fair value on a recurring basis	'
	The following tables present a reconciliation for all assets and liabilities measured at fair value on a recurring basis, excluding accrued interest components, using significant unobservable inputs (Level 3) for the year ended March 31, 2014 (amounts in thousands):
	Year ended March 31, 2014		Auction Rate				Corporate			Contingent				Total Gains
			Securities				Debt			Consideration				(Losses)
	Balance at March 31, 2013		$	33,791			$	6,190		$	(19,100	)		$	—
	Total gains (losses) (realized and unrealized):
	Included in earnings		1,101				—			(1,370		)		(269		)
	Included in other comprehensive income		(332		)		—			—				(332		)
	Purchases, sales, issuances, and settlements, net		(24,735		)		—			20,470				—
	Balance at March 31, 2014		$	9,825			$	6,190		$	—			$	(601	)
Fair Value, by Balance Sheet Grouping	'
	Assets measured at fair value on a recurring basis are presented/classified on the condensed consolidated balance sheets at June 30, 2014 as follows (amounts in thousands):
		Quoted Prices				Significant			Significant				Total
		in Active				Other			Unobservable				Balance
		Markets for				Observable			Inputs
		Identical				Inputs			(Level 3)
		Instruments				(Level 2)
		(Level 1)
	Assets
	Cash and cash equivalents	$	8,051			$	609,719		$	—			$	617,770
	Short-term investments	—				1,142,091			—				1,142,091
	Long-term investments	—				511,524			16,015				527,539
	Total assets measured at fair value	$	8,051			$	2,263,334		$	16,015			$	2,287,400
	Assets measured at fair value on a recurring basis are presented/classified in the condensed consolidated balance sheets at March 31, 2014 as follows (amounts in thousands):
		Quoted Prices				Significant			Significant				Total
		in Active				Other			Unobservable				Balance
		Markets for				Observable			Inputs
		Identical				Inputs			(Level 3)
		Instruments				(Level 2)
		(Level 1)
	Assets
	Cash and cash equivalents	$	192,159			$	274,444		$	—			$	466,603
	Short-term investments	—				878,182			—				878,182
	Long-term investments	—				782,697			16,015				798,712
	Total assets measured at fair value	$	192,159			$	1,935,323		$	16,015			$	2,143,497

Accounts_Receivable_Tables

Accounts Receivable (Tables)	3 Months Ended
	Jun. 30, 2014
Accounts Receivable, Net [Abstract]	'
Accounts Receivable Schedule	'
	Accounts receivable consists of the following (amounts in thousands):
		June 30, 2014		March 31, 2014
	Trade accounts receivable	$	287,415	$	243,383
	Other	2,300		1,940
		289,715		245,323
	Less allowance for doubtful accounts	3,016		2,918
		$	286,699	$	242,405

Inventories_Tables

Inventories (Tables)	3 Months Ended
	Jun. 30, 2014
Inventory Disclosure [Abstract]	'
Components of inventories	'
	The components of inventories consist of the following (amounts in thousands):
		June 30, 2014		March 31, 2014
	Raw materials	$	11,154	$	9,734
	Work in process	189,419		179,692
	Finished goods	63,932		73,299
		$	264,505	$	262,725

Property_Plant_and_Equipment_T

Property, Plant and Equipment (Tables)	3 Months Ended
	Jun. 30, 2014
Property, Plant and Equipment [Abstract]	'
Property, Plant and Equipment	'
	Property, plant and equipment consists of the following (amounts in thousands):
		June 30, 2014		March 31, 2014
	Land	$	70,720	$	55,624
	Building and building improvements	414,826		411,149
	Machinery and equipment	1,495,018		1,465,255
	Projects in process	81,109		68,991
		2,061,673		2,001,019
	Less accumulated depreciation and amortization	1,491,765		1,469,052
		$	569,908	$	531,967

Intangible_Assets_and_Goodwill1

Intangible Assets and Goodwill (Tables)	3 Months Ended
	Jun. 30, 2014
Goodwill and Intangible Assets Disclosure [Abstract]	'
Intangible Assets	'
	Intangible assets consist of the following (amounts in thousands):
			June 30, 2014
			Gross Amount			Accumulated Amortization			Net Amount
	Developed technology		$	493,248		$	(137,650	)	$	355,598
	Customer-related		213,500			(125,580		)	87,920
	Trademarks and trade names		15,730			(7,721		)	8,009
	Backlog		25,710			(24,885		)	825
	In-process technology		45,335			—			45,335
	Distribution rights		5,585			(5,193		)	392
	Covenants not to compete		400			(400		)	—
			$	799,508		$	(301,429	)	$	498,079
			March 31, 2014
			Gross Amount			Accumulated Amortization			Net Amount
	Developed technology		$	402,669		$	(117,222	)	$	285,447
	Customer-related		195,800			(109,170		)	86,630
	Trademarks and trade names		15,730			(7,118		)	8,612
	Backlog		24,610			(24,610		)	—
	In-process technology		64,396			—			64,396
	Distribution rights		5,585			(5,171		)	414
	Covenants not to compete		400			(400		)	—
			$	709,190		$	(263,691	)	$	445,499
Projected Amortization Expense	'
	The following is an expected amortization schedule for the intangible assets for the remainder of fiscal 2015 through fiscal 2019, absent any future acquisitions or impairment charges (amounts in thousands):
	Year ending	Projected Amortization
	March 31,	Expense
	2015	$114,073
	2016	107,173
	2017	71,652
	2018	57,187
	2019	48,964
Goodwill Activity	'
	Goodwill activity for the three months ended June 30, 2014 was as follows (amounts in thousands):
		Semiconductor Products			Technology
		Reporting Unit			Licensing
					Reporting Unit
	Balance at March 31, 2014	$	256,897		$	19,200
	Additions due to the acquisition of Supertex	133,713			—
	Adjustments due to other acquisitions	75			—
	Balance at June 30, 2014	$	390,685		$	19,200

Comprehensive_Income_Tables

Comprehensive Income (Tables)	3 Months Ended
	Jun. 30, 2014
Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Schedule of Accumulated Other Comprehensive Income (Loss)	'
	The following table presents the changes in the components of accumulated other comprehensive income (AOCI) for the three months ended June 30, 2014 (amounts in thousands):
		Unrealized				Minimum			Foreign		Total
		holding gains (losses)				pension			Currency
		available-for-sale securities				liability
	Balance at March 31, 2014	$	(528	)		$	140		$	1,439	$	1,051
	Other comprehensive income before reclassifications	3,060				—			—		3,060
	Amounts reclassified from accumulated other comprehensive income (loss)	(22		)		—			—		(22		)
	Net other comprehensive income	3,038				—			—		3,038
	Balance at June 30, 2014	$	2,510			$	140		$	1,439	$	4,089
Reclassification out of Accumulated Other Comprehensive Income	'
	The table below details where reclassifications of realized transactions out of AOCI are recorded on the Condensed Consolidated Statements of Income (amounts in thousands):
			Three Months Ended
			June 30,
	Description of AOCI Component		2014				2013			Related Statement
										of Income Line
	Unrealized gains on available-for-sale securities		$	34			$	50		Other income
	Taxes		(12		)		—			Provision for income taxes
	Reclassification of realized transactions, net of taxes		$	22			$	50		Net income

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	3 Months Ended
	Jun. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Share-based compensation expense	'
	The following table presents the details of the Company's share-based compensation expense (amounts in thousands):
		Three Months Ended
		June 30,
		2014			2013
	Cost of sales	$	2,055	(1)	$	1,969	(1)
	Research and development	6,309			5,690
	Selling, general and administrative	4,957			4,997
	Pre-tax effect of share-based compensation	13,321			12,656
	Income tax benefit	1,420			1,402
	Net income effect of share-based compensation	$	11,901		$	11,254

Net_income_per_common_share_Ta

Net income per common share (Tables)	3 Months Ended
	Jun. 30, 2014
Earnings Per Share [Abstract]	'
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	'
	The following table sets forth the computation of basic and diluted net income per common share (in thousands, except per share amounts):
		Three Months Ended
		June 30,
		2014		2013
	Net income	$	89,909	$	78,579
	Weighted average common shares outstanding	200,187		196,950
	Dilutive effect of stock options and RSUs	3,792		3,672
	Dilutive effect of convertible debt	20,548		11,644
	Weighted average common and potential common shares outstanding	224,527		212,266
	Basic net income per common share	$	0.45	$	0.4
	Diluted net income per common share	$	0.4	$	0.37

Basis_of_Presentation_Details

Basis of Presentation (Details)	Jun. 30, 2014
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]	'
Percentage Of Outstanding Stock Of All Subsidiaries Owned	100.00%

Business_Acquisitions_Narrativ

Business Acquisitions (Narrative) (Details) (USD $)	3 Months Ended		0 Months Ended	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Apr. 01, 2014	Jun. 30, 2014	Apr. 01, 2014
			Supertex Inc.	Supertex Inc.	Supertex Inc.
Business Acquisition [Line Items]	'	'	'	'	'
Tendered offer price per share	'	'	'	'	$33
Total consideration transferred	'	'	$391,800,000	'	'
Non cash consideration of certain share-based payment awards	'	'	1,600,000	'	'
Cash and short-term investments acquired	'	'	155,800,000	'	'
Amount of cash paid, net of cash and short-term investments acquired	375,365,000	0	234,400,000	'	'
Net deferred tax liability for future amortization expense of acquired intangible assets	'	'	'	'	22,800,000
Revenue of acquiree included in statement of income since the acquisition date	'	'	'	17,800,000	'
Net income (loss) of acquiree included in statement of income since the acquisition date	'	'	'	$17,700,000	'

Business_Acquisitions_Schedule

Business Acquisitions (Schedule of Preliminary Allocation of Purchase Price) (Details) (USD $)	Jun. 30, 2014	Mar. 31, 2014	Apr. 01, 2014
In Thousands, unless otherwise specified			Supertex Inc.
Business Acquisition [Line Items]	'	'	'
Cash and cash equivalents	'	'	$14,790
Short-term investments	'	'	140,984
Accounts receivable, net	'	'	7,047
Inventories	'	'	27,630
Prepaid expenses	'	'	1,493
Deferred tax assets	'	'	3,997
Other current assets	'	'	16,113
Property, plant and equipment, net	'	'	15,679
Goodwill	409,885	276,097	133,713
Purchased intangible assets	'	'	89,600
Other assets	'	'	325
Total assets acquired	'	'	451,371
Accounts payable	'	'	-8,481
Accrued liabilities	'	'	-19,345
Long-term income tax payable	'	'	-3,796
Deferred tax liability	'	'	-27,972
Total liabilities assumed	'	'	-59,594
Purchase price allocated	'	'	$391,777

Business_Acquisitions_Schedule1

Business Acquisitions (Schedule of Purchased Intangible Assets) (Details) (Supertex Inc., USD $)	0 Months Ended
In Thousands, unless otherwise specified	Apr. 01, 2014
Business Acquisition [Line Items]	'
Purchased Intangible Assets	$89,600
Core/developed technology	'
Business Acquisition [Line Items]	'
Useful Life	'10 years
Purchased Intangible Assets	68,900
In-process technology	'
Business Acquisition [Line Items]	'
Useful Life	'10 years
Purchased Intangible Assets	1,900
Customer-related	'
Business Acquisition [Line Items]	'
Useful Life	'2 years
Purchased Intangible Assets	17,700
Backlog	'
Business Acquisition [Line Items]	'
Useful Life	'1 year
Purchased Intangible Assets	$1,100

Business_Acquisitions_Schedule2

Business Acquisitions (Schedule of Proforma Information) (Details) (Supertex Inc., USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Supertex Inc.	'	'
Business Acquisition [Line Items]	'	'
Net sales	$531,345	$476,521
Net income	$105,505	$60,964
Basic earnings per share	$0.53	$0.31
Diluted earnings per share	$0.47	$0.29

Recently_Issued_Accounting_Pro1

Recently Issued Accounting Pronouncements (Details) (USD $)	Jun. 30, 2014
In Millions, unless otherwise specified
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
unrecognized tax benefit presented as a reduction to deferred tax assets for net operating loss carryforward and other tax credit carryforwards	$51.90

Special_Charges_Details

Special Charges (Details) (Unusual or Infrequent Item [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Unusual or Infrequent Item [Member]	'	'
Unusual or Infrequent Item [Line Items]	'	'
Other Nonrecurring Expense	$0.30	$1.70

Segment_Information_Details

Segment Information (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Segment reporting information [Line Items]	'	'
Net sales	$528,876	$462,792
Gross Profit	306,519	266,574
Semiconductor products [Member]	'	'
Segment reporting information [Line Items]	'	'
Net sales	508,439	440,274
Gross Profit	286,082	244,056
Technology licensing [Member]	'	'
Segment reporting information [Line Items]	'	'
Net sales	20,437	22,518
Gross Profit	$20,437	$22,518

Summary_of_Available_for_Sale_

Summary of Available for Sale (Details) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014
Summary of available-for-sale securities [Line Items]	'	'
Available-for-sale, adjusted cost	$1,667,120	$1,677,422
Available-for-sale, gross unrealized gains	3,994	3,462
Available-for-sale, gross unrealized losses	-1,484	-3,990
Available-for-sale, estimated fair value	1,669,630	1,676,894
Government agency bonds [Member]	'	'
Summary of available-for-sale securities [Line Items]	'	'
Available-for-sale, adjusted cost	684,090	684,451
Available-for-sale, gross unrealized gains	318	114
Available-for-sale, gross unrealized losses	-1,108	-3,171
Available-for-sale, estimated fair value	683,300	681,394
Municipal bonds [Member]	'	'
Summary of available-for-sale securities [Line Items]	'	'
Available-for-sale, adjusted cost	41,347	41,622
Available-for-sale, gross unrealized gains	225	101
Available-for-sale, gross unrealized losses	-7	-14
Available-for-sale, estimated fair value	41,565	41,709
Auction rate securities [Member]	'	'
Summary of available-for-sale securities [Line Items]	'	'
Available-for-sale, adjusted cost	9,825	9,825
Available-for-sale, gross unrealized gains	0	0
Available-for-sale, gross unrealized losses	0	0
Available-for-sale, estimated fair value	9,825	9,825
Corporate bonds and debt [Member]	'	'
Summary of available-for-sale securities [Line Items]	'	'
Available-for-sale, adjusted cost	931,858	941,524
Available-for-sale, gross unrealized gains	3,451	3,247
Available-for-sale, gross unrealized losses	-369	-805
Available-for-sale, estimated fair value	$934,940	$943,966

Investments_AFS_Details

Investments AFS (Details) (USD $)	Jun. 30, 2014	Mar. 31, 2014
Investments [Abstract]	'	'
Amount of short-term investments	$1,142,091,000	$878,182,000
Amount of long-term investments	527,539,000	798,712,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	519,600,000	'
Amount of corporate debt securities with no contractual maturity excluded from estimated fair value of available-for-sale securities	$6,200,000	'

AFS_Debt_Maturities_Details

AFS, Debt Maturities (Details) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014
Schedule of available-for-sale securities, debt maturities [Line Items]	'	'
Available-for-sale, adjusted cost	$1,667,120	$1,677,422
Available-for-sale, gross unrealized gains	3,994	3,462
Available-for-sale, gross unrealized losses	-1,484	-3,990
Available-for-sale, estimated fair value	1,669,630	1,676,894
Due in one year or less [Member]	'	'
Schedule of available-for-sale securities, debt maturities [Line Items]	'	'
Available-for-sale, adjusted cost	199,349	'
Available-for-sale, gross unrealized gains	841	'
Available-for-sale, gross unrealized losses	-6	'
Available-for-sale, estimated fair value	200,184	'
Due after one year and through five years [Member]	'	'
Schedule of available-for-sale securities, debt maturities [Line Items]	'	'
Available-for-sale, adjusted cost	1,324,320	'
Available-for-sale, gross unrealized gains	3,100	'
Available-for-sale, gross unrealized losses	-762	'
Available-for-sale, estimated fair value	1,326,658	'
Due after five years and through ten years [Member]	'	'
Schedule of available-for-sale securities, debt maturities [Line Items]	'	'
Available-for-sale, adjusted cost	127,436	'
Available-for-sale, gross unrealized gains	53	'
Available-for-sale, gross unrealized losses	-716	'
Available-for-sale, estimated fair value	126,773	'
Due after ten years [Member]	'	'
Schedule of available-for-sale securities, debt maturities [Line Items]	'	'
Available-for-sale, adjusted cost	9,825	'
Available-for-sale, gross unrealized gains	0	'
Available-for-sale, gross unrealized losses	0	'
Available-for-sale, estimated fair value	9,825	'
Total Maturities [Member]	'	'
Schedule of available-for-sale securities, debt maturities [Line Items]	'	'
Available-for-sale, adjusted cost	1,660,930	'
Available-for-sale, gross unrealized gains	3,994	'
Available-for-sale, gross unrealized losses	-1,484	'
Available-for-sale, estimated fair value	$1,663,440	'

Measured_on_Recurring_Basis_De

Measured on Recurring Basis (Details) (USD $)

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2013

Mar. 31, 2013

Jun. 30, 2014

Jun. 30, 2014

Jun. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Mar. 31, 2014

Insurance Sector Auction Rate Securities [Member]

Insurance Sector Auction Rate Securities [Member]

Insurance Sector Auction Rate Securities [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Minimum [Member]

Maximum [Member]

Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Money Market Fund Deposits Fair Value Disclosure

$8,051,000

$192,159,000

'

'

'

'

'

$8,051,000

$192,159,000

$0

$0

$0

$0

Corporate Bonds and Debt Fair Value Disclosure

934,940,000

943,966,000

'

'

'

'

'

0

0

928,750,000

937,776,000

6,190,000

6,190,000

Government Agency Bonds Fair Value Disclosure

683,300,000

681,394,000

'

'

'

'

'

0

0

683,300,000

681,394,000

0

0

Cash Deposit Accounts Fair Value Disclosure

609,719,000

274,444,000

'

'

'

'

'

0

0

609,719,000

274,444,000

0

0

Municipal Bonds Fair Value Disclosure

41,565,000

41,709,000

'

'

'

'

'

0

0

41,565,000

41,709,000

0

0

Auction Rate Securities Fair Value Disclosure

9,825,000

9,825,000

'

'

'

'

'

0

0

0

0

9,825,000

9,825,000

Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash and cash equivalents

617,770,000

466,603,000

403,231,000

528,334,000

'

'

'

8,051,000

192,159,000

609,719,000

274,444,000

0

0

Short-term investments

1,142,091,000

878,182,000

'

'

'

'

'

0

0

1,142,091,000

878,182,000

0

0

Long-term investments

527,539,000

798,712,000

'

'

'

'

'

0

0

511,524,000

782,697,000

16,015,000

16,015,000

Total assets measured at fair value

2,287,400,000

2,143,497,000

'

'

'

'

'

8,051,000

192,159,000

2,263,334,000

1,935,323,000

16,015,000

16,015,000

Available-for-sale Securities, Other Disclosure Items [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

Value of auction rate securities for which recent auctions were unsuccessful

'

'

'

'

9,800,000

'

'

'

'

'

'

'

'

Discount rate

'

'

'

'

'

2.00%

2.50%

'

'

'

'

'

'

Auction Rate Securities Par Value

'

'

'

'

$22,400,000

'

'

'

'

'

'

'

'

Liquidity risk premium (percentage)

'

'

'

'

'

9.10%

29.50%

'

'

'

'

'

'

Anticipated liquidity horizon

'

'

'

'

'

'7 years

'10 years

'

'

'

'

'

'

Unobservable_Input_Reconciliat

Unobservable Input Reconciliation Assets (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014
Fair value, assets measured on recurring basis, unobservable input reconciliation [Line Items]	'
Total Gains (Losses)	($601)
Auction rate securities [Member]	'
Fair value, assets measured on recurring basis, unobservable input reconciliation [Line Items]	'
Fair value, measurement with unobservable inputs reconciliation, beginning	33,791
Included in earnings	1,101
Included in other comprehensive income (loss)	-332
Purchases, sales, issuances, and settlements, net	-24,735
Fair value, measurement with unobservable inputs reconciliation, ending	9,825
Corporate Debt [Member]	'
Fair value, assets measured on recurring basis, unobservable input reconciliation [Line Items]	'
Fair value, measurement with unobservable inputs reconciliation, beginning	6,190
Included in earnings	0
Included in other comprehensive income (loss)	0
Purchases, sales, issuances, and settlements, net	0
Fair value, measurement with unobservable inputs reconciliation, ending	6,190
Total Gains (Losses) [Member]	'
Fair value, assets measured on recurring basis, unobservable input reconciliation [Line Items]	'
Included in earnings	-269
Included in other comprehensive income (loss)	-332
Purchases, sales, issuances, and settlements, net	'

Unobservable_Input_Reconciliat1

Unobservable Input Reconciliation Liabilities (Details) (Contingent consideration [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014
Contingent consideration [Member]	'
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'
Fair value, measurements with unobservable inputs reconciliation, beginning	$19,100
Included in earnings	-1,370
Purchases, sales, issuances, and settlements, net	-20,470
Fair value, measurements with unobservable inputs reconciliation, ending	$0

Fair_Value_of_Financial_Instru1

Fair Value of Financial Instruments (Details) (USD $)	Jun. 30, 2014	Mar. 31, 2014
In Millions, unless otherwise specified
Fair Value Disclosures [Abstract]	'	'
Fair value of junior subordinated convertible debentures based on the trading price of the bonds	$2,197	$2,138

Accounts_Receivable_Details

Accounts Receivable (Details) (USD $)	Jun. 30, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Receivable amounts	$289,715	$245,323
Less allowance for doubtful accounts	3,016	2,918
Accounts receivable, net	286,699	242,405
Trade Accounts Receivable [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Receivable amounts	287,415	243,383
Other Receivables [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Receivable amounts	$2,300	$1,940

Inventories_Details

Inventories (Details) (USD $)	Jun. 30, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Inventory Disclosure [Abstract]	'	'
Raw materials	$11,154	$9,734
Work in process	189,419	179,692
Finished goods	63,932	73,299
Inventory, Net	$264,505	$262,725

Property_Plant_and_Equipment_D

Property, Plant and Equipment (Details) (USD $)	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Mar. 31, 2014
Property, Plant and Equipment [Line Items]	'	'	'
Property, plant, and equipment costs	$2,061,673,000	'	$2,001,019,000
Accumulated depreciation	1,491,765,000	'	1,469,052,000
Property, plant and equipment, net	569,908,000	'	531,967,000
Depreciation expense	23,300,000	21,400,000	'
Land [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Property, plant, and equipment costs	70,720,000	'	55,624,000
Buildings and building improvements [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Property, plant, and equipment costs	414,826,000	'	411,149,000
Machinery and equipment [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Property, plant, and equipment costs	1,495,018,000	'	1,465,255,000
Projects in progress [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Property, plant, and equipment costs	$81,109,000	'	$68,991,000

Intangible_Assets_by_Major_Cla

Intangible Assets, by Major Class (Details) (USD $)

3 Months Ended

3 Months Ended

0 Months Ended

3 Months Ended

Jun. 30, 2014

Jun. 30, 2013

Mar. 31, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Jun. 30, 2014

Apr. 01, 2014

Apr. 01, 2014

Apr. 01, 2014

Apr. 01, 2014

Apr. 01, 2014

Jun. 30, 2014

Jun. 30, 2013

Jun. 30, 2014

Jun. 30, 2013

Core/developed technology

Core/developed technology

Customer Relationships [Member]

Customer Relationships [Member]

Trademarks and trade names [Member]

Trademarks and trade names [Member]

Backlog [Member]

Backlog [Member]

In-process technology [Member]

In-process technology [Member]

Distribution rights [Member]

Distribution rights [Member]

Covenants not to compete [Member]

Covenants not to compete [Member]

Minimum [Member]

Maximum [Member]

Supertex Inc. [Member]

Supertex Inc. [Member]

Supertex Inc. [Member]

Supertex Inc. [Member]

Supertex Inc. [Member]

Cost of Sales [Member]

Cost of Sales [Member]

Operating Expense [Member]

Operating Expense [Member]

Core/developed technology

Customer Relationships [Member]

Backlog [Member]

In-process technology [Member]

Finite-Lived Intangible Assets, Net [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Gross Amount

$799,508,000

'

$709,190,000

$493,248,000

$402,669,000

$213,500,000

$195,800,000

$15,730,000

$15,730,000

$25,710,000

$24,610,000

$45,335,000

$64,396,000

$5,585,000

$5,585,000

$400,000

$400,000

'

'

'

'

'

'

'

'

'

'

'

Accumulated Amortization

-301,429,000

'

-263,691,000

-137,650,000

-117,222,000

-125,580,000

-109,170,000

-7,721,000

-7,118,000

-24,885,000

-24,610,000

0

0

-5,193,000

-5,171,000

-400,000

-400,000

'

'

'

'

'

'

'

'

'

'

'

Net Amount

498,079,000

'

445,499,000

355,598,000

285,447,000

87,920,000

86,630,000

8,009,000

8,612,000

825,000

0

45,335,000

64,396,000

392,000

414,000

0

0

'

'

'

'

'

'

'

'

'

'

'

In-process technology reaching technological feasibility and reclassified

21,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Purchased Intangible Assets

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

89,600,000

68,900,000

17,700,000

1,100,000

1,900,000

'

'

'

'

Useful Life

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'1 year

'15 years

'

'10 years

'2 years

'1 year

'

'

'

'

'

Minimum expected useful life of finite lived intangible assets (in years)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'1 year

'15 years

'

'10 years

'2 years

'1 year

'

'

'

'

'

Amortization of Intangible Assets

37,700,000

28,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,000,000

1,300,000

36,700,000

27,600,000

Impairment of Intangible Assets

406,000

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Future Amortization Expense, Remainder of Fiscal Year

114,073,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Future Amortization Expense, Year Two

107,173,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Future Amortization Expense, Year Three

71,652,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Future Amortization Expense, Year Four

57,187,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Future Amortization Expense, Year Five

$48,964,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Goodwill_by_Reporting_Segment_

Goodwill by Reporting Segment (Details) (USD $)	Jun. 30, 2014	Mar. 31, 2014	Apr. 01, 2014	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2014	Jun. 30, 2014
In Thousands, unless otherwise specified			Supertex Inc. [Member]	Semiconductor products [Member]	Semiconductor products [Member]	Semiconductor products [Member]	Semiconductor products [Member]	Technology licensing [Member]	Technology licensing [Member]	Technology licensing [Member]	Technology licensing [Member]
						Supertex Inc. [Member]	Other acquisitions			Supertex Inc. [Member]	Other acquisitions
Goodwill [Roll Forward]	'	'	'	'	'	'	'	'	'	'	'
Goodwill, beginning balance	$409,885	$276,097	$133,713	$390,685	$256,897	'	'	$19,200	$19,200	'	'
Additions due to business combination	'	'	'	'	'	133,713	75	'	'	0	0
Goodwill, ending balance	$409,885	$276,097	$133,713	$390,685	$256,897	'	'	$19,200	$19,200	'	'

Income_tax_Details

Income tax (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Income Tax Disclosure [Abstract]	'	'
Effective Income Tax Rate	16.00%	13.00%
Unrecognized Tax Benefits	$196.40	'
Unrecognized Tax Benefits, Period Increase (Decrease)	16.4	'
unrecognized tax benefit presented as a reduction to deferred tax assets for net operating loss carryforward and other tax credit carryforwards	$51.90	'

2125_Junior_subordinated_conve1

2.125% Junior subordinated convertible debentures (Details) (USD $)	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Mar. 31, 2014
Debt Instrument [Line Items]	'	'	'
Carrying value of debentures	$374,227,000	'	$371,873,000
Amortization of Debt Discount (Premium)	2,365,000	2,161,000	'
Junior subordinated convertible debentures due 2037 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Principal amount of junior subordinated convertible debentures	1,150,000,000	'	'
Interest rate of junior subordinated convertible debentures	2.13%	'	'
Due date of junior subordinated convertible debentures	15-Dec-37	'	'
Conversion rate, in shares, of junior subordinated convertible debt (in shares per $1,000)	29.2783	'	'
Principal amount of junior subordinated convertible debentures used as conversion unit	1,000	'	'
Convertible Debt Instrument Initial Conversion Price Per Share	$34.16	'	'
Debt Instrument, Convertible, Conversion Ratio	38.9573	'	'
Debt Instrument, Convertible, Conversion Price	$25.67	'	'
Long-term Debt, Contingent Payment of Interest, Percentage	0.50%	'	'
Carrying value of equity component of the debentures that were bifurcated into a liability and equity component	822,400,000	'	822,400,000
Estimated fair value of liability component of debentures at issuance date	327,600,000	'	'
Debt discount of estimated fair value of liability component of debentures	822,400,000	'	'
Amount of unamortized debt discount of debentures	774,900,000	'	777,200,000
Remaining period, in years, over which unamortized debt discount will be recognized as non-cash interest expense (in years)	'23 years 6 months	'	'
Amortization of Debt Discount (Premium)	2,400,000	2,200,000	'
Recognized amount of interest expense related to debentures	$6,100,000	$6,100,000	'
Minimum [Member] | Junior subordinated convertible debentures due 2037 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term Debt, Contingent Payment of Interest, Percentage	0.25%	'	'
Debt Instrument, Convertible, Trading Price	$40	'	'
Maximum [Member] | Junior subordinated convertible debentures due 2037 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term Debt, Contingent Payment of Interest, Percentage	0.50%	'	'
Debt Instrument, Convertible, Trading Price	$150	'	'

Credit_facility_Details

Credit facility (Details) (USD $)	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 27, 2013
Line of Credit Facility [Line Items]	'	'	'
Interest expense	$13,678,000	$11,856,000	'
Credit Agreement Maturity June 27, 2018 [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Initiation date	27-Jun-13	'	'
Credit agreement	'	'	2,000,000,000
Maturity Date	27-Jun-18	'	'
Increase option amount	'	'	300,000,000
Line of Credit Facility, Fair Value of Amount Outstanding	980,000,000	'	'
Debt discount	1,000,000	'	'
Interest expense	5,000,000	3,400,000	'
Short-term Debt, Weighted Average Interest Rate	1.65%	'	'
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Period for leverage ratio to determine interest rate spread	'preceding four fiscal quarter period	'	'
Interest rate spread on overdue principal in event of default (percentage)	'	'	2.00%
Interest rate spread on overdue amounts in event of default (percentage)	'	'	2.00%
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option1 [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Description of variable rate basis	'the highest of JPMorgan Chase Bank, N.A.'s prime rate, the federal funds rate plus a margin equal to 0.50% and the adjusted LIBOR rate for a 1-month interest period plus a margin equal to 1.00%	'	'
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option1 [Member] | Minimum [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Spread on variable rate (percentage)	0.25%	'	'
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option1 [Member] | Maximum [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Spread on variable rate (percentage)	1.25%	'	'
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option 2 [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Description of variable rate basis	'adjusted LIBOR rate (based on one, two, three, or six-month interest periods)	'	'
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option 2 [Member] | Minimum [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Spread on variable rate (percentage)	1.25%	'	'
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option 2 [Member] | Maximum [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Spread on variable rate (percentage)	2.25%	'	'
Credit Agreement Maturity June 27, 2018 [Member] | Term loan [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Credit agreement	'	'	350,000,000
Line of Credit Facility, Fair Value of Amount Outstanding	345,600,000	'	'
Credit Agreement Maturity June 27, 2018 [Member] | Revolving credit facility [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Credit agreement	'	'	1,650,000,000
Line of Credit Facility, Fair Value of Amount Outstanding	634,400,000	'	'
Credit Agreement Maturity June 27, 2018 [Member] | Foreign Line of Credit [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Credit agreement	'	'	125,000,000
Credit Agreement Maturity June 27, 2018 [Member] | Standby Letters of Credit [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Credit agreement	'	'	35,000,000
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit Facility Swingline Loan Sublimit [Member]	'	'	'
Line of Credit Facility [Line Items]	'	'	'
Credit agreement	'	'	$25,000,000

Contingencies_Details

Contingencies (Details) (USD $)	Jun. 30, 2014
In Millions, unless otherwise specified
SST acquisition [Member]	'
Loss contingencies [Line Items]	'
Contingent liabilities outstanding	$5.70
Indemnification agreement [Member]	'
Loss contingencies [Line Items]	'
Loss contingencies, estimate of possible loss	$132

Derivative_Instruments_Details

Derivative Instruments (Details)	3 Months Ended
	Jun. 30, 2014
Derivative [Line Items]	'
Percentage Of Company Sales Denominated In Us Dollars	99.00%

Comprehensive_Income_Schedule_

Comprehensive Income (Schedule of Changes in the Components of AOCI) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014
Changes in the components of AOCI	'
Balance at March 31, 2014	$1,051
Other comprehensive income before reclassifications	3,060
Amounts reclassified from accumulated other comprehensive income (loss)	-22
Net other comprehensive income	3,038
Balance at June 30, 2014	4,089
Unrealized holding gains (losses) on available-for-sale securities	'
Changes in the components of AOCI	'
Balance at March 31, 2014	-528
Other comprehensive income before reclassifications	3,060
Amounts reclassified from accumulated other comprehensive income (loss)	-22
Net other comprehensive income	3,038
Balance at June 30, 2014	2,510
Minimum pension liability	'
Changes in the components of AOCI	'
Balance at March 31, 2014	140
Other comprehensive income before reclassifications	0
Amounts reclassified from accumulated other comprehensive income (loss)	0
Net other comprehensive income	0
Balance at June 30, 2014	140
Foreign Currency	'
Changes in the components of AOCI	'
Balance at March 31, 2014	1,439
Other comprehensive income before reclassifications	0
Amounts reclassified from accumulated other comprehensive income (loss)	0
Net other comprehensive income	0
Balance at June 30, 2014	$1,439

Comprehensive_Income_Schedule_1

Comprehensive Income (Schedule of Reclassifications of Recognized Transactions out of AOCI) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'
Other Nonoperating Income (Expense)	$13	$126
Income Tax Expense (Benefit)	17,082	11,757
Net income	89,909	78,579
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'
Other Nonoperating Income (Expense)	34	50
Income Tax Expense (Benefit)	12	0
Net income	$22	$50

ShareBased_Compensation_Detail

Share-Based Compensation (Details) (USD $)	3 Months Ended
	Jun. 30, 2014		Jun. 30, 2013
Stock-based compensation expense [Line Items]	'		'
Allocated Share-based Compensation Expense	$11,901,000		$11,254,000
Inventory [Member]	'		'
Stock-based compensation expense [Line Items]	'		'
Amount of share-based compensation expense capitalized to inventory	1,700,000		1,400,000
Cost of Sales [Member]	'		'
Stock-based compensation expense [Line Items]	'		'
Allocated Share-based Compensation Expense	2,055,000	[1]	1,969,000	[1]
Research and development [Member]	'		'
Stock-based compensation expense [Line Items]	'		'
Allocated Share-based Compensation Expense	6,309,000		5,690,000
Selling, General and Administrative Expenses [Member]	'		'
Stock-based compensation expense [Line Items]	'		'
Allocated Share-based Compensation Expense	4,957,000		4,997,000
Pre-tax effect of share based compensation [Member]	'		'
Stock-based compensation expense [Line Items]	'		'
Allocated Share-based Compensation Expense	13,321,000		12,656,000
Income tax benefit [Member]	'		'
Stock-based compensation expense [Line Items]	'		'
Allocated Share-based Compensation Expense	$1,420,000		$1,402,000
[1]	During the three months ended JuneB 30, 2014, $1.7 million of share-based compensation expense was capitalized to inventory and $2.1 million of previously capitalized share-based compensation expenses in inventory was sold. During the three months ended JuneB 30, 2013, $1.4 million of share-based compensation expense was capitalized to inventory and $2.0 million of previously capitalized share-based compensation expense in inventory was sold.

Net_income_per_common_share_De

Net income per common share (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]	'	'
Net income	$89,909	$78,579
Weighted average common shares outstanding	200,187,000	196,950,000
Dilutive effect of stock options and RSUs	3,792,000	3,672,000
Dilutive effect of convertible debt	20,547,832	11,644,236
Weighted average common and potential common shares outstanding	224,527,000	212,266,000
Basic net income per common share	$0.45	$0.40
Diluted net income per common share	$0.40	$0.37
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (amount per share)	$25.75	$26.66
Number of antidilutive option shares (in shares)	0	50,198

Dividends_Details

Dividends (Details) (USD $)	0 Months Ended	3 Months Ended		0 Months Ended
In Millions, except Per Share data, unless otherwise specified	Jun. 03, 2014	Jun. 30, 2014	Jun. 30, 2013	Jul. 31, 2014
				Subsequent Event [Member]
Dividends [Abstract]	'	'	'	'
Dividend per share paid during period	$0.36	'	'	'
Cash Dividend	$71.20	'	'	$71.40
Subsequent Event [Line Items]	'	'	'	'
Dividends declared per common share	'	$0.36	$0.35	$0.36
Total amount of expected dividend payment	$71.20	'	'	$71.40

Subsequent_Event_Details

Subsequent Event (Details) (Subsequent Event, ISSC Technologies Corporation)	0 Months Ended				0 Months Ended
In Millions, except Share data, unless otherwise specified	Jul. 14, 2014	Jul. 14, 2014	Jul. 14, 2014	Jul. 14, 2014	Jul. 14, 2014
	USD ($)	TWD	USD ($)	TWD	Minimum
Subsequent Event [Line Items]	'	'	'	'	'
Total number of shares tendered	57,228,225	57,228,225	'	'	27,300,429
Percentage of outstanding shares acquired	'	'	83.46%	83.46%	'
Tendered offer price per share	'	'	$4.74	143	'
Total equity value	$328.50	9,900	'	'	'
Total enterprise value	287.1	8,700	'	'	'
Cash and short-term investments acquired	$41.40	1,200	'	'	'