Microchip Technology (MCHP) 10-Q 3 Feb 15 2015 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information Document	9 Months Ended
	Dec. 31, 2014	Jan. 21, 2015
DEI Information [Abstract]
Entity Registrant Name	MICROCHIP TECHNOLOGY INC
Entity Central Index Key	827054
Current Fiscal Year End Date	-28
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding		201,448,608

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (unaudited) (USD $)	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
ASSETS
Cash and cash equivalents	$456,339	$466,603
Short-term investments	666,119	878,182
Accounts receivable, net	242,595	242,405
Inventories	276,143	262,725
Prepaid expenses	35,111	31,756
Deferred tax assets	50,490	67,490
Assets held for sale	13,985	0
Other current assets	42,697	20,238
Total current assets	1,783,479	1,969,399
Property, plant and equipment, net	577,123	531,967
Long-term investments	1,107,224	798,712
Goodwill	565,290	276,097
Intangible assets, net	551,210	445,499
Other assets	44,591	45,956
Total assets	4,628,917	4,067,630
LIABILITIES AND EQUITY
Accounts payable	76,933	74,050
Accrued liabilities	104,389	96,731
Short-term borrowings	17,500	17,500
Deferred Income on Shipments to Distributors	154,264	147,798
Total current liabilities	353,086	336,079
Junior convertible debentures	379,263	371,873
Long-term line of credit	644,375	300,000
Long-term borrowings, net	318,457	331,385
Long-term income tax payable	138,388	179,966
Long-term deferred tax liability	468,842	375,316
Other long-term liabilities	44,228	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 201,444,488 shares outstanding at December 31, 2014; 218,789,994 shares issued and 200,002,736 shares outstanding at March 31, 2014	201	200
Additional paid-in capital	1,252,902	1,244,583
Common stock held in treasury: 17,345,506 shares at December 31, 2014; 18,787,258 shares at March 31, 2014	-534,562	-577,382
Accumulated other comprehensive income	15,563	1,051
Retained earnings	1,522,185	1,467,009
Microchip Technology stockholders' equity	2,256,289	2,135,461
Noncontrolling interests	25,989	0
Total equity	2,282,278	2,135,461
Total liabilities and equity	$4,628,917	$4,067,630

CONDENSED_CONSOLIDATED_BALANCE1

CONDENSED CONSOLIDATED BALANCE SHEETS CONDENSED CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) (USD $)	Dec. 31, 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	201,444,488	200,002,736
Treasury Stock, Shares	17,345,506	18,787,258

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF INCOME (unaudited) (USD $)	3 Months Ended				9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2014		Dec. 31, 2013
Income Statement
Net sales	$528,710		$482,372		$1,603,829		$1,437,833
Cost of sales (1)	226,751	[1]	199,652	[1]	687,897	[1]	599,676	[1]
Gross profit	301,959		282,720		915,932		838,157
Operating expenses:
Research and development (1)	88,697	[1]	76,341	[1]	261,881	[1]	227,680	[1]
Selling, general and administrative (1)	66,668	[1]	66,856	[1]	207,037	[1]	201,934	[1]
Amortization of acquired intangible assets	47,582		21,804		129,659		73,225
Special charges	1,003		801		2,082		2,491
Total operating expenses	203,950		165,802		600,659		505,330
Operating income	98,009		116,918		315,273		332,827
(Losses) gains on equity method investments	-62		150		-129		-211
Other income (expense):
Interest income	4,924		4,241		14,197		12,176
Interest expense	-14,223		-12,545		-41,920		-36,755
Other (expense) income, net	-2,457		3,824		-3,535		6,093
Income before income taxes	86,191		112,588		283,886		314,130
Income tax provision	1,393		7,187		17,141		30,344
Net income	84,798		105,401		266,745		283,786
Less: Net loss attributable to noncontrolling interests	1,259		0		2,862		0
Net income attributable to Microchip Technology	86,057		105,401		269,607		283,786
Basic net income per common share attributable to Microchip Technology stockholders	$0.43		$0.53		$1.34		$1.43
Diluted net income per common share attributable to Microchip Technology stockholders	$0.39		$0.48		$1.20		$1.31
Dividends declared per common share	$0.36		$0.35		$1.07		$1.06
Basic common shares outstanding	201,203		198,759		200,673		197,845
Diluted common shares outstanding	223,487		219,089		224,433		215,943
Allocated Share-based Compensation Expense	11,187		12,209		36,528		36,874
Cost of Sales [Member]
Other income (expense):
Allocated Share-based Compensation Expense	2,290	[2]	1,841	[2]	6,985	[2]	5,674	[2]
Research and Development Expense [Member]
Other income (expense):
Allocated Share-based Compensation Expense	7,075		6,141		20,645		18,762
Selling, General and Administrative Expenses [Member]
Other income (expense):
Allocated Share-based Compensation Expense	$5,454		$5,737		$15,783		$16,939
[1]	Includes share-based compensation expense as follows:Cost of sales 2,290 1,841 6,985 5,674 Research and development 7,075 6,141 20,645 18,762 Selling, general and administrative 5,454 5,737 15,783 16,939
[2]	During the three and nine months ended DecemberB 31, 2014, $1.7 million and $5.0 million, respectively, of share-based compensation expense was capitalized to inventory and $2.3 million and $7.0 million, respectively, of previously capitalized share-based compensation expense in inventory was sold. During the three and nine months ended DecemberB 31, 2013, $1.9 million and $5.7 million, respectively, of share-based compensation expense was capitalized to inventory and $1.8 million and $5.7 million, respectively, of previously capitalized share-based compensation expense in inventory was sold.

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF INCOME (PARENTHETICAL) (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2014		Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$11,187		$12,209		$36,528		$36,874
Cost of Sales [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	2,290	[1]	1,841	[1]	6,985	[1]	5,674	[1]
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	7,075		6,141		20,645		18,762
Selling General And Administrative Member
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$5,454		$5,737		$15,783		$16,939
[1]	During the three and nine months ended DecemberB 31, 2014, $1.7 million and $5.0 million, respectively, of share-based compensation expense was capitalized to inventory and $2.3 million and $7.0 million, respectively, of previously capitalized share-based compensation expense in inventory was sold. During the three and nine months ended DecemberB 31, 2013, $1.9 million and $5.7 million, respectively, of share-based compensation expense was capitalized to inventory and $1.8 million and $5.7 million, respectively, 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		9 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Net income	$84,798	$105,401	$266,745	$283,786
Less: Net loss attributable to noncontrolling interests	1,259	0	2,862	0
Net income attributable to Microchip Technology	86,057	105,401	269,607	283,786
Unrealized holding gains (losses), net of tax effect of $12,380, $0, $12,392 and $497, respectively	19,844	59	19,439	-8,011
Reclassification of realized transactions, net of tax effect of $0, $0, $12 and $776, respectively	-73	-113	-157	-1,503
Change in net foreign currency translation adjustment	1,046	0	-5,188	0
Other comprehensive income (loss), net of taxes	20,817	-54	14,094	-9,514
Less: Other comprehensive (income) loss attributable to noncontrolling interests	-149	0	866	0
Other comprehensive income (loss) attributable to Microchip Technology	20,668	-54	14,960	-9,514
Comprehensive income	105,615	105,347	280,839	274,272
Less: Comprehensive loss attributable to noncontrolling interests	-1,110	0	-3,728	0
Comprehensive income attributable to Microchip Technology	$106,725	$105,347	$284,567	$274,272

CONDENSED_CONSOLIDATED_STATEME3

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (PARENTHETICAL) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$12,380	$0	$12,392	$497

CONDENSED_CONSOLIDATED_STATEME4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (unaudited) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net income	$266,745	$283,786
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	205,112	143,704
Deferred income taxes	5,795	24,190
Share-based compensation expense related to equity incentive plans	43,413	41,375
Excess tax benefit from share-based compensation	-1,100	0
Convertible debt derivatives - revaluation and amortization	79	-449
Amortization of debt discount on convertible debentures	7,311	6,682
Amortization of debt issuance costs	1,632	1,416
Losses on equity method investments	129	211
Loss on write-down of fixed assets	285	0
Impairment of intangible assets	1,861	350
Amortization of premium on available-for-sale investments	7,561	8,067
Special income, net	0	-999
Gain on shares of acquired company	0	-2,438
Changes In Operating Assets And Liabilities
Decrease in accounts receivable	15,449	5,624
Decrease (increase) in inventories	28,684	-30,588
Increase in deferred income on shipments to distributors	6,466	4,363
Decrease in accounts payable and accrued liabilities	-39,001	-21,870
Change in other assets and liabilities	-7,749	9,799
Net cash provided by operating activities	542,672	473,223
Cash flows from investing activities
Purchases of available-for-sale investments	-721,861	-950,560
Sales and maturities of available-for-sale investments	821,160	584,186
Acquisition of ISSC, net of cash acquired	-252,469	0
Purchase of additional controlling interest in ISSC	-22,934	0
Acquisition of Supertex, net of cash acquired	-375,365	0
Other business acquisitions, net of cash acquired	0	-11,187
Investments in other assets	-5,274	-7,462
Proceeds from sale of assets	0	16,200
Capital expenditures	-120,014	-79,536
Net cash used in investing activities	-676,757	-448,359
Cash flows from financing activities:
Repayments of revolving loan under previous credit facility	0	-650,000
Repayments of revolving loan under new credit facility	-427,900	-153,500
Proceeds from borrowings on revolving loan under previous credit facility	0	30,000
Proceeds from borrowings on revolving loan under new credit facility	772,275	453,500
Proceeds from issuance of long-term borrowings	0	350,000
Repayments of long-term borrowings	-13,125	0
Deferred financing costs	0	-7,515
Payment of cash dividends	-214,431	-210,322
Proceeds from sale of common stock	20,829	42,517
Tax payments related to shares withheld for vested restricted stock units	-14,276	-17,765
Contingent consideration payment	0	-14,700
Capital lease payments	-450	-313
Excess tax benefit from share-based compensation	1,100	0
Net cash provided by (used in) financing activities	124,022	-178,098
Effect of foreign exchange rate changes on cash and cash equivalents	-201	0
Net decrease in cash and cash equivalents	-10,264	-153,234
Cash and cash equivalents at beginning of period	466,603	528,334
Cash and cash equivalents at end of period	$456,339	$375,100

Basis_of_Presentation_Notes

Basis of Presentation (Notes)	9 Months Ended
	Dec. 31, 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 majority-owned subsidiaries (the Company).  The Company owns 100% of the outstanding stock in all of its subsidiaries with the exception of its recent acquisition of ISSC Technologies Corporation (ISSC) as further discussed in Note 2. The noncontrolling interests in the Company's net income from ISSC have been excluded from net income attributable to the Company in the Company's condensed consolidated statements of income. All intercompany balances and transactions have been eliminated in consolidation.
	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 nine months ended December 31, 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.

Business_Acquisitions_Notes

Business Acquisitions (Notes)	9 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Business Acquisitions	Business Acquisitions
	Acquisition of ISSC
	On July 17, 2014, the Company acquired an 83.5% interest in Taiwan based ISSC, a leading provider of low power Bluetooth and advanced wireless solutions for the Internet of Things (IoT) market. The total purchase price paid for the 83.5% interest was approximately $267.6 million and was financed with existing cash and investment balances. The Company's primary reason for this acquisition was to expand the Company's range of solutions, products and capabilities in the wireless and IoT areas by extending its served available market. The Company acquired the 83.5% ownership interest through a tender offer process and expects to acquire the remaining shares through a follow-on merger which is expected to close in the first quarter of fiscal 2016. As of December 31, 2014, the Company's ownership percentage in ISSC was approximately 91.1%.
	The acquisition was accounted for under the acquisition method of accounting, with the Company identified as the acquirer. Since the Company's acquired ownership interest in ISSC represents a controlling interest, the operating results of ISSC have been included in the Company's condensed consolidated financial statements as of the closing date of the acquisition with the noncontrolling interest deducted to arrive at net income. The fair value of the noncontrolling interest at the acquisition date was calculated based on the expected purchase price of the remaining shares available. As the Company purchases additional shares of ISSC, the noncontrolling interest will be reduced and any gain or loss on the shares purchased will be reflected in the stockholders' equity of the Company. Under the acquisition method of accounting, the aggregate amount of consideration paid by the Company was allocated to ISSC's net tangible assets and intangible assets based on their estimated fair values as of July 17, 2014.  The excess of the purchase price over the value of the net tangible assets and intangible assets was recorded to goodwill. The factors contributing to the recognition of goodwill were based upon the Company's conclusion that there are strategic and synergistic benefits that are expected to be realized from the acquisition. The goodwill has been allocated to the Company's semiconductor products reporting segment.  None of the goodwill related to the ISSC 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 the 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, including adjustments to the purchase price allocation from the originally reported figures at September 30, 2014, to the net assets acquired based on their estimated fair values as of July 17, 2014, as well as the associated estimated useful lives of the acquired intangible assets at that date (amounts in thousands):
	Assets acquired	Previously Reported September 30, 2014				Adjustments			31-Dec-14
	Cash and cash equivalents	$	15,120			$	—		$	15,120
	Short-term investments	27,063				—			27,063
	Accounts receivable, net	8,792				—			8,792
	Inventories	19,160				(2,618		)	16,542
	Prepaid expenses and other current assets	2,501				—			2,501
	Property, plant and equipment, net	2,637				—			2,637
	Goodwill	152,243				2,156			154,399
	Purchased intangible assets	147,800				—			147,800
	Other assets	1,370				—			1,370
	Total assets acquired	376,686				(462		)	376,224
	Liabilities assumed
	Accounts payable	(9,860		)		—			(9,860		)
	Other current liabilities	(16,997		)		462			(16,535		)
	Long-term income tax payable	(4,402		)		—			(4,402		)
	Deferred tax liability	(25,126		)		—			(25,126		)
	Other long-term liabilities	(245		)		—			(245		)
	Total liabilities assumed	(56,630		)		462			(56,168		)
	Net assets acquired including noncontrolling interest	320,056				—			320,056
	Less: noncontrolling interest	(52,467		)		—			(52,467		)
	Net assets acquired	$	267,589			$	—		$	267,589
	The amount of cash paid by the Company, net of cash and short-term investments acquired from ISSC of approximately $42.2 million, was $225.4 million.
	Purchased Intangible Assets	Useful Life		1-Apr-14
		(in years)		(in thousands)
	Core/developed technology	10		$	68,900
	In-process technology	10		27,200
	Customer-related	3		51,100
	Backlog	1		600
				$	147,800
	Purchased intangible assets include core and developed technology, in-process technology, customer-related intangibles and acquisition-date backlog. The estimated fair values of the core and developed technology and in-process technology 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 ISSC'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 ISSC's projected revenues. An analysis of expected attrition and revenue growth for existing customers was prepared from ISSC'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 ISSC 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 $25.1 million was established as a net deferred tax liability for the future amortization of the intangible assets.
	The amount of ISSC net sales and net loss attributable to the Company included in the Company's condensed consolidated statements of income for the three months ended December 31, 2014 was approximately $8.7 million and $10.0 million, respectively. The amount of ISSC net sales and net loss attributable to the Company included in the Company's condensed consolidated statements of income for the nine months ended December 31, 2014 was approximately $25.6 million and $18.2 million, respectively. The amount of ISSC net sales in the three months ended December 31, 2014 was negatively impacted by approximately $7.1 million due to the Company changing the contractual relationships with the ISSC distribution network to a sell through revenue recognition model.
	The following unaudited pro-forma consolidated results of operations for the three and nine months ended December 31, 2014 and 2013 assume the ISSC 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							Nine Months Ended
		December 31,							December 31,
		2014				2013			2014			2013
	Net sales	$	528,710			$	497,585		$	1,626,183		$	1,490,776
	Net income attributable to Microchip Technology	86,683				97,470			265,412			260,386
	Net income attributable to Microchip Technology common stockholders per share - basic	$	0.43			$	0.49		$	1.32		$	1.32
	Net income attributable to Microchip Technology common stockholders per share - diluted	$	0.39			$	0.44		$	1.18		$	1.21
	Acquisition of Supertex
	On April 1, 2014, the Company acquired Supertex Inc., 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 factors contributing to the recognition of goodwill were based upon the Company's conclusion that there are strategic and synergistic benefits that are expected to be realized from the acquisition. 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 the 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, including adjustments to the purchase price allocation from the originally reported figures at June 30, 2014, to the net assets acquired based on their estimated fair values as of April 1, 2014 (amounts in thousands):
	Assets acquired	Previously Reported June 30, 2014				Adjustments			31-Dec-14
	Cash and cash equivalents	$	14,790			$	—		$	14,790
	Short-term investments	140,984				—			140,984
	Accounts receivable, net	7,047				—			7,047
	Inventories	27,630				—			27,630
	Prepaid expenses	1,493				—			1,493
	Deferred tax assets	3,997				—			3,997
	Other current assets	16,113				—			16,113
	Property, plant and equipment, net	15,679				—			15,679
	Goodwill	133,713				3,465			137,178
	Purchased intangible assets	89,600				—			89,600
	Other assets	325				—			325
	Total assets acquired	451,371				3,465			454,836
	Liabilities assumed
	Accounts payable	(8,481		)		—			(8,481		)
Accrued liabilities	(19,345		)		(25		)	(19,370		)
Long-term income tax payable	(3,796		)		—			(3,796		)
Deferred tax liability	(27,972		)		(3,440		)	(31,412		)
Total liabilities assumed	(59,594		)		(3,465		)	(63,059		)
Net assets acquired	$	391,777			$	—		$	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 technology, customer-related intangibles and acquisition-date backlog. The estimated fair values of the core and developed technology and in-process technology 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 included in the Company's condensed consolidated statements of income for the three months ended December 31, 2014 was approximately $18.6 million. The amount of Supertex net sales included in the Company's condensed consolidated statements of income for the nine months ended December 31, 2014 was approximately $53.0 million. The operations of Supertex were fully integrated into the Company's operations as of July 1, 2014 and as such, cost of sales and operating expenses were no longer segregated in the three or nine months ended December 31, 2014.
The following unaudited pro-forma consolidated results of operations for the three and nine months ended December 31, 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							Nine Months Ended
	December 31,							December 31,
	2014				2013			2014			2013
Net sales	$	528,710			$	499,722		$	1,606,298		$	1,486,661
Net income	87,392				99,741			291,288			251,976
Basic earnings per share	$	0.43			$	0.5		$	1.45		$	1.27
Diluted earnings per share	$	0.39			$	0.46		$	1.3		$	1.17

Recently_Issued_Accounting_Pro

Recently Issued Accounting Pronouncements (Notes)	9 Months Ended
	Dec. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements
	In June 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-12, Compensation - Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could be Achieved after the Requisite Service Period.  The amendments in this ASU provide explicit guidance on whether a performance target contained in a share-based payment award that could be achieved after the requisite service period should be treated (i) as a performance condition that affects vesting or (ii) as a nonvesting condition that affects the grant-date fair value of the award.  The amendments require that a performance target that affects vesting, and that could be achieved after the requisite service period, be treated as a performance condition rather than as a nonvesting condition.  Accordingly, such performance targets are not reflected in the estimation of the grant date fair value of the award.  Compensation cost should be recognized in the period in which it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the period(s) for which the requisite service has already been rendered.  If the performance target becomes probable of being achieved before the end of the requisite service period, the remaining unrecognized compensation cost should be recognized prospectively over the remaining service period.  The total amount of compensation cost recognized during and after the requisite service period should reflect the number of awards that are expected to vest and should be adjusted to reflect those awards that ultimately vest.  The amendments in this update are effective for annual periods beginning after December 15, 2015, and interim periods within those annual periods.  Early adoption is permitted.  The Company does not anticipate adoption of this ASU will have a material impact on its consolidated financial statements.
	In July 2013, FASB issued ASU 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. There was no income statement impact to the Company as a result of adopting this accounting standard.
	In May 2014, the FASB issued ASU 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 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 with 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)	9 Months Ended
	Dec. 31, 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 $1.0 million and $2.1 million for the three and nine months ended December 31, 2014, respectively, and $0.8 million and $2.5 million for the three and nine months ended December 31, 2013, respectively.

Segment_Information_Notes

Segment Information (Notes)	9 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Segment Information	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 and nine months ended December 31, 2014 (amounts in thousands):
		Three Months Ended				Nine Months Ended
		December 31, 2014				December 31, 2014
		Net Sales		Gross Profit		Net Sales		Gross Profit
	Semiconductor products	$	505,763	$	279,012	$	1,537,861	$	849,964
	Technology licensing	22,947		22,947		65,968		65,968
		$	528,710	$	301,959	$	1,603,829	$	915,932
	The following table represents net sales and gross profit for each segment for the three and nine months ended December 31, 2013 (amounts in thousands):
		Three Months Ended				Nine Months Ended
		December 31, 2013				December 31, 2013
		Net Sales		Gross Profit		Net Sales		Gross Profit
	Semiconductor products	$	458,298	$	258,646	$	1,366,415	$	766,739
	Technology licensing	24,074		24,074		71,418		71,418
		$	482,372	$	282,720	$	1,437,833	$	838,157

Investments_Notes

Investments (Notes)	9 Months Ended
	Dec. 31, 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 December 31, 2014 (amounts in thousands):
		Available-for-sale Securities
		Adjusted		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair Value
				Gains			Losses
	Government agency bonds	$	736,615	$	113		$	(1,866	)	$	734,862
	Municipal bonds	45,140		74			(32		)	45,182
	Auction rate securities	9,825		—			—			9,825
	Time deposits (1)	8,699		—			—			8,699
	Corporate bonds and debt	938,331		927			(1,397		)	937,861
	Marketable equity securities	3,600		33,314			—			36,914
		$	1,742,210	$	34,428		$	(3,295	)	$	1,773,343
	(1) Time deposits in various financial institutions with maturities greater than three months that will mature within one year.
	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 December 31, 2014, the Company's available-for-sale securities are presented on the condensed consolidated balance sheets as short-term investments of $666.1 million and long-term investments of $1,107.2 million.  At March 31, 2014, the Company's available-for-sale 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.
	The Company's marketable equity securities consist of an investment in Hua Hong Semiconductor Limited (Hua Hong), which effected its initial public offering on the Hong Kong stock exchange on October 15, 2014. This investment was previously classified as a non-marketable cost-method investment, and had a carrying value of $3.6 million.
	The following tables show all investments in an unrealized loss position for which an other-than-temporary impairment has not been recognized and the related gross unrealized losses and fair value, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position (amounts in thousands):
		31-Dec-14
		Less than 12 Months					12 Months or Greater						Total
		Fair Value		Unrealized Loss			Fair Value			Unrealized Loss			Fair Value		Unrealized Loss
	Government agency bonds	$	568,466	$	(1,561	)	$	64,695		$	(305	)	$	633,161	$	(1,866	)
	Municipal bonds	13,533		(32		)	—			—			13,533		(32		)
	Corporate bonds and debt	460,372		(1,363		)	5,988			(34		)	466,360		(1,397		)
		$	1,042,371	$	(2,956	)	$	70,683		$	(339	)	$	1,113,054	$	(3,295	)
		31-Mar-14
		Less than 12 Months					12 Months or Greater						Total
		Fair Value		Unrealized Loss			Fair Value			Unrealized Loss			Fair Value		Unrealized Loss
	Government agency bonds	$	522,159	$	(3,172	)	$	—		$	—		$	522,159	$	(3,172	)
	Municipal bonds	2,625		(13		)	1,196			(1		)	3,821		(14		)
	Corporate bonds and debt	256,717		(804		)	—			—			256,717		(804		)
		$	781,501	$	(3,989	)	$	1,196		$	(1	)	$	782,697	$	(3,990	)
	Management does not believe any of the unrealized losses represent an other-than-temporary impairment based on its evaluation of available evidence as of December 31, 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 December 31, 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 December 31, 2014, by contractual maturity, excluding marketable equity securities of $36.9 million and corporate debt of $6.2 million, which have 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	$	216,444	$	258		$	(9	)	$	216,693
	Due after one year and through five years	1,428,901		835			(3,081		)	1,426,655
	Due after five years and through ten years	77,250		21			(205		)	77,066
	Due after ten years	9,825		—			—			9,825
		$	1,732,420	$	1,114		$	(3,295	)	$	1,730,239
	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 and nine-month periods ended December 31, 2014 and 2013.

Fair_Value_Measurements_Notes

Fair Value Measurements (Notes)	9 Months Ended
	Dec. 31, 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 mutual funds. 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 December 31, 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	$	51,677			$	—		$	—			$	51,677
	Marketable equity securities	36,914				—			—				36,914
	Corporate bonds and debt	—				931,671			6,190				937,861
	Time deposits (1)	—				8,699			—				8,699
	Government agency bonds	—				734,862			—				734,862
	Deposit accounts	—				404,662			—				404,662
	Municipal bonds	—				45,182			—				45,182
	Auction rate securities	—				—			9,825				9,825
	Total assets measured at fair value	$	88,591			$	2,125,076		$	16,015			$	2,229,682
	(1) Time deposits in various financial institutions with maturities greater than three months that will mature within one year.
	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 and nine-month periods ended December 31, 2014 or the year ended March 31, 2014.
	At December 31, 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 December 31, 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 Losses
			Securities				Debt			Consideration
	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		$	—
	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 December 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	$	51,677			$	404,662		$	—			$	456,339
	Short-term investments	36,914				629,205			—				666,119
	Long-term investments	—				1,091,209			16,015				1,107,224
	Total assets measured at fair value	$	88,591			$	2,125,076		$	16,015			$	2,229,682
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 during the three and nine-month periods ended December 31, 2014 and December 31, 2013.

Fair_Value_of_Financial_Instru

Fair Value of Financial Instruments (Notes)	9 Months Ended
	Dec. 31, 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 December 31, 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 December 31, 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 $2.051 billion at December 31, 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. See Note 16 for more information regarding the Company's junior subordinated convertible debentures.

Accounts_Receivable_Notes

Accounts Receivable (Notes)	9 Months Ended
	Dec. 31, 2014
Accounts Receivable, Net [Abstract]
Accounts Receivable	Accounts Receivable
	Accounts receivable consists of the following (amounts in thousands):
		December 31, 2014		March 31, 2014
	Trade accounts receivable	$	242,437	$	243,383
	Other	3,069		1,940
		245,506		245,323
	Less allowance for doubtful accounts	2,911		2,918
		$	242,595	$	242,405

Inventories_Notes

Inventories (Notes)	9 Months Ended
	Dec. 31, 2014
Inventory Disclosure [Abstract]
Inventories	Inventories
	The components of inventories consist of the following (amounts in thousands):
		December 31, 2014		March 31, 2014
	Raw materials	$	14,301	$	9,734
	Work in process	190,573		179,692
	Finished goods	71,269		73,299
		$	276,143	$	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.

Assets_Held_for_Sale_Notes

Assets Held for Sale (Notes)	9 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment Assets Held-for-sale Disclosure [Abstract]
Assets Held for Sale	Assets Held for Sale
	During the three months ended December 31, 2014, the Company began to actively market property it acquired as part of the Supertex acquisition.   The Company expects to sell the property within one year.  As of December 31, 2014, the Company classified the assets as held for sale on its condensed consolidated balance sheet at its fair value of approximately $14.3 million, net of the estimated cost to sell of approximately $0.3 million.

Property_Plant_and_Equipment_N

Property, Plant and Equipment (Notes)	9 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment
	Property, plant and equipment consists of the following (amounts in thousands):
		December 31, 2014		March 31, 2014
	Land	$	55,624	$	55,624
	Building and building improvements	430,695		411,149
	Machinery and equipment	1,549,999		1,465,255
	Projects in process	75,800		68,991
		2,112,118		2,001,019
	Less accumulated depreciation and amortization	1,534,995		1,469,052
		$	577,123	$	531,967
	Depreciation expense attributed to property, plant and equipment was $24.7 million and $72.3 million for the three and nine months ended December 31, 2014, respectively, and $22.2 million and $66.7 million for the three and nine months ended December 31, 2013, respectively.

Noncontrolling_Interests_Notes

Noncontrolling Interests (Notes)	9 Months Ended
	Dec. 31, 2014
Noncontrolling Interest [Abstract]
Noncontrolling Interest Disclosure [Text Block]	Noncontrolling Interests
	The following table presents the changes in the components of noncontrolling interests for the nine months ended December 31, 2014 (amounts in thousands):
		Noncontrolling Interests
	Balance at March 31, 2014	$	—
	Additions due to acquisition of controlling interest in ISSC	52,467
	Net loss attributable to noncontrolling interests	(2,862		)
	Other comprehensive loss attributable to noncontrolling interests	(866		)
	Purchase of additional interests	(23,054		)
	Other	304
	Balance at December 31, 2014	$	25,989
	The following table presents the effect of changes in the Company's ownership interest in ISSC on the Company's stockholders' equity for the nine months ended December 31, 2014 (amounts in thousands):
		Nine Months Ended
		31-Dec-14
	Net income attributable to Microchip Technology stockholders	$	269,607
	Increase in paid-in capital for purchase of additional interests	568
	Increase in paid-in capital for converted stock options	1,094
	Transfers from noncontrolling interest	1,662
	Change from net income attributable to Microchip Technology stockholders and transfers from noncontrolling interest	$	271,269

Intangible_Assets_and_Goodwill

Intangible Assets and Goodwill (Notes)	9 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets and Goodwill	Intangible Assets and Goodwill
	Intangible assets consist of the following (amounts in thousands):
			December 31, 2014
			Gross Amount			Accumulated Amortization			Net Amount
	Developed technology		$	563,272		$	(185,391	)	$	377,881
	Customer-related		263,969			(170,719		)	93,250
	Trademarks and trade names		15,730			(8,926		)	6,804
	Backlog		26,302			(25,818		)	484
	In-process technology		72,442			—			72,442
	Distribution rights		5,585			(5,236		)	349
	Covenants not to compete		400			(400		)	—
			$	947,700		$	(396,490	)	$	551,210
			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.  During the nine months ended December 31, 2014, $20.7 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	$48,377
	2016	146,898
	2017	91,833
	2018	69,488
	2019	62,732
	Amortization expense attributed to intangible assets was $48.6 million and $132.8 million for the three and nine months ended December 31, 2014, respectively. Amortization expense attributed to intangible assets was $23.0 million and $77.0 million for the three and nine months ended December 31, 2013, respectively.  In the three and nine months ended December 31, 2014, approximately $0.9 million and $2.9 million was charged to cost of sales, respectively, and approximately $47.7 million and $129.9 million was charged to operating expenses, respectively.  In the three and nine months ended December 31, 2013, approximately $1.2 million and $3.7 million was charged to cost of sales, respectively, and approximately $21.8 million and $73.3 million was charged to operating expenses, respectively.  The Company recognized impairment charges of $1.3 million and $1.9 million in the three and nine months ended December 31, 2014, respectively. The Company recognized impairment charges of $0.4 million in the nine months ended December 31, 2013. The Company did not recognize any impairment charges in the three months ended December 31, 2013.
	Goodwill activity for the nine months ended December 31, 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	137,178			—
	Additions due to acquisition of controlling interest in ISSC	154,399			—
	Adjustments due to other acquisitions	625			—
	Foreign currency translation adjustments	(3,009		)	—
	Balance at December 31, 2014	$	546,090		$	19,200
	At December 31, 2014, $546.1 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 December 31, 2014, the Company had never recorded an impairment charge against its goodwill balance.

Income_taxes_Notes

Income taxes (Notes)	9 Months Ended
	Dec. 31, 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 6.0% for the nine-month period ended December 31, 2014 and 9.7% for the nine-month period ended December 31, 2013.  The Company's effective tax rate for nine-month period ended December 31, 2014 is lower compared to the prior year primarily due to closure of statute of limitations, certain audit settlements with taxing authorities and a change in judgment regarding certain state valuation allowances. During the three-month period ended December 31, 2014, approximately $1.9 million of prior year tax positions were released which increased each of the basic and diluted net income per common share for the three-month period ended December 31, 2014 by approximately $0.01. During the nine-month period ended December 31, 2014, approximately $9.3 million of prior year tax positions were released which increased each of the basic and diluted net income per common share for the nine-month period ended December 31, 2014 by approximately $0.04. 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.
	At December 31, 2014, the Company had $222.0 million of unrecognized tax benefits.  Unrecognized tax benefits increased by $42.0 million compared to March 31, 2014 primarily as a result of unrecognized tax benefits from the Company's acquisitions of Supertex and ISSC, the ongoing accrual for uncertain tax positions and the accrual of deficiency interest on these positions. The majority of the increase in the uncertain tax position does not result in a change in the Company's effective tax rate. The Company evaluated the impact of the adoption of ASU 2013-11 on its condensed consolidated financial statements and determined that $83.6 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 Standard Microsystems Corporation's (SMSC) 2011 and 2012 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)	9 Months Ended
	Dec. 31, 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 December 31, 2014, the holders of the debentures have the right to convert their debentures between January 1, 2015 and March 31, 2015 because for at least 20 trading days during the 30 consecutive trading day period ending on December 31, 2014, the Company's common stock had a last reported sale price greater than 130% of the conversion price. As of December 31, 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 39.5749 shares of common stock per $1,000 of principal amount of debentures, representing a conversion price of approximately $25.27 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 December 31, 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 $769.9 million at December 31, 2014 and $777.2 million at March 31, 2014.  The carrying value of the debentures was $379.3 million at December 31, 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 years.  In the three and nine months ended December 31, 2014, the Company recognized $2.5 million and $7.3 million, respectively, in non-cash interest expense related to the amortization of the debt discount.  In the three and nine months ended December 31, 2013, the Company recognized $2.3 million and $6.7 million, respectively, in non-cash interest expense related to the amortization of the debt discount.  The Company recognized $6.1 million and $18.3 million of interest expense related to the 2.125% coupon on the debentures in each of the three and nine-month periods ended December 31, 2014 and December 31, 2013, respectively.

Credit_facility_Notes

Credit facility (Notes)	9 Months Ended
	Dec. 31, 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 December 31, 2014, $981.3 million of borrowings were outstanding under the Credit Agreement consisting of $644.4 million of a revolving line of credit and $336.9 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 $5.3 million and $15.4 million in the three and nine months ended December 31, 2014, respectively, and approximately $4.1 million and $11.5 million in the three and nine months ended December 31, 2013, respectively. 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 December 31, 2014 related to the Credit Agreement was 1.67%. 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 December 31, 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)	9 Months Ended
	Dec. 31, 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 $138 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 December 31, 2014.

Derivative_Instruments_Notes

Derivative Instruments (Notes)	9 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	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 December 31, 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 and nine months ended December 31, 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)	9 Months Ended
	Dec. 31, 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 nine months ended December 31, 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 (loss) before reclassifications	19,439			—			(4,322		)		15,117
	Amounts reclassified from accumulated other comprehensive income (loss)	(157		)	—			—				(157		)
	Net other comprehensive income (loss)	19,282			—			(4,322		)		14,960
	Purchase of shares from noncontrolling interest	—			—			(448		)		(448		)
	Balance at December 31, 2014	$	18,754		$	140		$	(3,331	)		$	15,563
	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						Nine Months Ended
			December 31,						December 31,
	Description of AOCI Component		2014			2013			2014				2013			Related Statement
																of Income Line
	Unrealized gains on available-for-sale securities		$	73		$	113		$	169			$	2,279		Other income
	Taxes		—			—			(12		)		(776		)	Provision for income taxes
	Reclassification of realized transactions, net of taxes		$	73		$	113		$	157			$	1,503		Net income

ShareBased_Compensation_Notes

Share-Based Compensation (Notes)	9 Months Ended
	Dec. 31, 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						Nine Months Ended
		December 31,						December 31,
		2014			2013			2014			2013
	Cost of sales	$	2,290	(1)	$	1,841	(1)	$	6,985	(1)	$	5,674	(1)
	Research and development	7,075			6,141			20,645			18,762
	Selling, general and administrative	5,454			5,737			15,783			16,939
	Pre-tax effect of share-based compensation	14,819			13,719			43,413			41,375
	Income tax benefit	3,632			1,510			6,885			4,501
	Net income effect of share-based compensation	$	11,187		$	12,209		$	36,528		$	36,874
	(1) During the three and nine months ended December 31, 2014, $1.7 million and $5.0 million, respectively, of share-based compensation expense was capitalized to inventory and $2.3 million and $7.0 million, respectively, of previously capitalized share-based compensation expense in inventory was sold.  During the three and nine months ended December 31, 2013, $1.9 million and $5.7 million, respectively, of share-based compensation expense was capitalized to inventory and $1.8 million and $5.7 million, respectively, of previously capitalized share-based compensation expense in inventory was sold.

Net_income_per_common_share_No

Net income per common share (Notes)	9 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income per common share	Net Income Per Common Share Attributable to Microchip Technology Stockholders
	The following table sets forth the computation of basic and diluted net income per common share attributable to Microchip Technology stockholders (in thousands, except per share amounts):
		Three Months Ended				Nine Months Ended
		December 31,				December 31,
		2014		2013		2014		2013
	Net income attributable to Microchip Technology	$	86,057	$	105,401	$	269,607	$	283,786
	Weighted average common shares outstanding	201,203		198,759		200,673		197,845
	Dilutive effect of stock options and RSUs	3,396		3,834		3,652		3,882
	Dilutive effect of convertible debt	18,888		16,496		20,108		14,216
	Weighted average common and potential common shares outstanding	223,487		219,089		224,433		215,943
	Basic net income per common share attributable to Microchip Technology stockholders	$	0.43	$	0.53	$	1.34	$	1.43
	Diluted net income per common share attributable to Microchip Technology stockholders	$	0.39	$	0.48	$	1.2	$	1.31
	The Company computed basic earnings per common share attributable to its stockholders using net income available to common stockholders and the weighted average number of common shares outstanding during the period. The Company computed diluted earnings per common share attributable to its stockholders using net income available to 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 attributable to stockholders for the three and nine months ended December 31, 2014 includes 18,888,013 shares and 20,107,818 shares, respectively, issuable upon the exchange of debentures (see Note 16).  Diluted net income per common share attributable to stockholders for the three and nine months ended December 31, 2013 includes 16,496,384 shares and 14,215,573 shares, respectively, 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 and nine-month periods ended December 31, 2014 was $25.39 and $25.57, respectively. The weighted average conversion price per share used in calculating the dilutive effect of the convertible debt for the three and nine-month periods ended December 31, 2013 was $26.19 and $26.43, respectively.
	Weighted average common shares exclude the effect of option shares which are not dilutive.  For each of the three and nine months ended December 31, 2014, the number of option shares that were antidilutive was 46,959. There were no antidilutive option shares for the three and nine months ended December 31, 2013.

Dividends_Notes

Dividends (Notes)	9 Months Ended
	Dec. 31, 2014
Dividends [Abstract]
Dividends	Dividends
	A quarterly cash dividend of $0.3565 per share was paid on December 5, 2014 in the aggregate amount of $71.8 million.  Through the first nine months of fiscal 2015, cash dividends of $1.068 per share have been paid in the aggregate amount of $214.4 million. A quarterly cash dividend of $0.357 per share was declared on January 29, 2015 and will be paid on March 9, 2015 to stockholders of record as of February 23, 2015. The Company expects the March 2015 payment of its quarterly cash dividend to be approximately $72.0 million.

Business_Acquisitions_Tables

Business Acquisitions (Tables)	9 Months Ended
	Dec. 31, 2014
ISSC Technologies Corporation [Member]
Business Acquisition [Line Items]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The table below represents the preliminary allocation of the purchase price, including adjustments to the purchase price allocation from the originally reported figures at September 30, 2014, to the net assets acquired based on their estimated fair values as of July 17, 2014, as well as the associated estimated useful lives of the acquired intangible assets at that date (amounts in thousands):
	Assets acquired	Previously Reported September 30, 2014				Adjustments			31-Dec-14
	Cash and cash equivalents	$	15,120			$	—		$	15,120
	Short-term investments	27,063				—			27,063
	Accounts receivable, net	8,792				—			8,792
	Inventories	19,160				(2,618		)	16,542
	Prepaid expenses and other current assets	2,501				—			2,501
	Property, plant and equipment, net	2,637				—			2,637
	Goodwill	152,243				2,156			154,399
	Purchased intangible assets	147,800				—			147,800
	Other assets	1,370				—			1,370
	Total assets acquired	376,686				(462		)	376,224
	Liabilities assumed
	Accounts payable	(9,860		)		—			(9,860		)
	Other current liabilities	(16,997		)		462			(16,535		)
	Long-term income tax payable	(4,402		)		—			(4,402		)
	Deferred tax liability	(25,126		)		—			(25,126		)
	Other long-term liabilities	(245		)		—			(245		)
	Total liabilities assumed	(56,630		)		462			(56,168		)
	Net assets acquired including noncontrolling interest	320,056				—			320,056
	Less: noncontrolling interest	(52,467		)		—			(52,467		)
	Net assets acquired	$	267,589			$	—		$	267,589
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		27,200
	Customer-related	3		51,100
	Backlog	1		600
				$	147,800
Business Acquisition, Pro Forma Information	The following unaudited pro-forma consolidated results of operations for the three and nine months ended December 31, 2014 and 2013 assume the ISSC 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							Nine Months Ended
		December 31,							December 31,
		2014				2013			2014			2013
	Net sales	$	528,710			$	497,585		$	1,626,183		$	1,490,776
	Net income attributable to Microchip Technology	86,683				97,470			265,412			260,386
	Net income attributable to Microchip Technology common stockholders per share - basic	$	0.43			$	0.49		$	1.32		$	1.32
	Net income attributable to Microchip Technology common stockholders per share - diluted	$	0.39			$	0.44		$	1.18		$	1.21
Supertex Inc. [Member]
Business Acquisition [Line Items]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The table below represents the preliminary allocation of the purchase price, including adjustments to the purchase price allocation from the originally reported figures at June 30, 2014, to the net assets acquired based on their estimated fair values as of April 1, 2014 (amounts in thousands):
	Assets acquired	Previously Reported June 30, 2014				Adjustments			31-Dec-14
	Cash and cash equivalents	$	14,790			$	—		$	14,790
	Short-term investments	140,984				—			140,984
	Accounts receivable, net	7,047				—			7,047
	Inventories	27,630				—			27,630
	Prepaid expenses	1,493				—			1,493
	Deferred tax assets	3,997				—			3,997
	Other current assets	16,113				—			16,113
	Property, plant and equipment, net	15,679				—			15,679
	Goodwill	133,713				3,465			137,178
	Purchased intangible assets	89,600				—			89,600
	Other assets	325				—			325
	Total assets acquired	451,371				3,465			454,836
	Liabilities assumed
	Accounts payable	(8,481		)		—			(8,481		)
	Accrued liabilities	(19,345		)		(25		)	(19,370		)
	Long-term income tax payable	(3,796		)		—			(3,796		)
	Deferred tax liability	(27,972		)		(3,440		)	(31,412		)
	Total liabilities assumed	(59,594		)		(3,465		)	(63,059		)
	Net assets acquired	$	391,777			$	—		$	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 and nine months ended December 31, 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							Nine Months Ended
		December 31,							December 31,
		2014				2013			2014			2013
	Net sales	$	528,710			$	499,722		$	1,606,298		$	1,486,661
	Net income	87,392				99,741			291,288			251,976
	Basic earnings per share	$	0.43			$	0.5		$	1.45		$	1.27
	Diluted earnings per share	$	0.39			$	0.46		$	1.3		$	1.17

Segment_Information_Tables

Segment Information (Tables)	9 Months Ended
	Dec. 31, 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 and nine months ended December 31, 2014 (amounts in thousands):
		Three Months Ended				Nine Months Ended
		December 31, 2014				December 31, 2014
		Net Sales		Gross Profit		Net Sales		Gross Profit
	Semiconductor products	$	505,763	$	279,012	$	1,537,861	$	849,964
	Technology licensing	22,947		22,947		65,968		65,968
		$	528,710	$	301,959	$	1,603,829	$	915,932
	The following table represents net sales and gross profit for each segment for the three and nine months ended December 31, 2013 (amounts in thousands):
		Three Months Ended				Nine Months Ended
		December 31, 2013				December 31, 2013
		Net Sales		Gross Profit		Net Sales		Gross Profit
	Semiconductor products	$	458,298	$	258,646	$	1,366,415	$	766,739
	Technology licensing	24,074		24,074		71,418		71,418
		$	482,372	$	282,720	$	1,437,833	$	838,157

Investments_Tables

Investments (Tables)	9 Months Ended
	Dec. 31, 2014
Investments [Abstract]
Summary of available-for-sale securities	The following is a summary of available-for-sale securities at December 31, 2014 (amounts in thousands):
		Available-for-sale Securities
		Adjusted		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair Value
				Gains			Losses
	Government agency bonds	$	736,615	$	113		$	(1,866	)	$	734,862
	Municipal bonds	45,140		74			(32		)	45,182
	Auction rate securities	9,825		—			—			9,825
	Time deposits (1)	8,699		—			—			8,699
	Corporate bonds and debt	938,331		927			(1,397		)	937,861
	Marketable equity securities	3,600		33,314			—			36,914
		$	1,742,210	$	34,428		$	(3,295	)	$	1,773,343
	(1) Time deposits in various financial institutions with maturities greater than three months that will mature within one year.
	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 available-for-sale securities in a continuous unrealized loss position	The following tables show all investments in an unrealized loss position for which an other-than-temporary impairment has not been recognized and the related gross unrealized losses and fair value, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position (amounts in thousands):
		31-Dec-14
		Less than 12 Months					12 Months or Greater						Total
		Fair Value		Unrealized Loss			Fair Value			Unrealized Loss			Fair Value		Unrealized Loss
	Government agency bonds	$	568,466	$	(1,561	)	$	64,695		$	(305	)	$	633,161	$	(1,866	)
	Municipal bonds	13,533		(32		)	—			—			13,533		(32		)
	Corporate bonds and debt	460,372		(1,363		)	5,988			(34		)	466,360		(1,397		)
		$	1,042,371	$	(2,956	)	$	70,683		$	(339	)	$	1,113,054	$	(3,295	)
		31-Mar-14
		Less than 12 Months					12 Months or Greater						Total
		Fair Value		Unrealized Loss			Fair Value			Unrealized Loss			Fair Value		Unrealized Loss
	Government agency bonds	$	522,159	$	(3,172	)	$	—		$	—		$	522,159	$	(3,172	)
	Municipal bonds	2,625		(13		)	1,196			(1		)	3,821		(14		)
	Corporate bonds and debt	256,717		(804		)	—			—			256,717		(804		)
		$	781,501	$	(3,989	)	$	1,196		$	(1	)	$	782,697	$	(3,990	)
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 December 31, 2014, by contractual maturity, excluding marketable equity securities of $36.9 million and corporate debt of $6.2 million, which have 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	$	216,444	$	258		$	(9	)	$	216,693
	Due after one year and through five years	1,428,901		835			(3,081		)	1,426,655
	Due after five years and through ten years	77,250		21			(205		)	77,066
	Due after ten years	9,825		—			—			9,825
		$	1,732,420	$	1,114		$	(3,295	)	$	1,730,239

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Dec. 31, 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 December 31, 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	$	51,677			$	—		$	—			$	51,677
	Marketable equity securities	36,914				—			—				36,914
	Corporate bonds and debt	—				931,671			6,190				937,861
	Time deposits (1)	—				8,699			—				8,699
	Government agency bonds	—				734,862			—				734,862
	Deposit accounts	—				404,662			—				404,662
	Municipal bonds	—				45,182			—				45,182
	Auction rate securities	—				—			9,825				9,825
	Total assets measured at fair value	$	88,591			$	2,125,076		$	16,015			$	2,229,682
	(1) Time deposits in various financial institutions with maturities greater than three months that will mature within one year.
	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 Losses
			Securities				Debt			Consideration
	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		$	—
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 December 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	$	51,677			$	404,662		$	—			$	456,339
	Short-term investments	36,914				629,205			—				666,119
	Long-term investments	—				1,091,209			16,015				1,107,224
	Total assets measured at fair value	$	88,591			$	2,125,076		$	16,015			$	2,229,682
	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)	9 Months Ended
	Dec. 31, 2014
Accounts Receivable, Net [Abstract]
Accounts Receivable Schedule	Accounts receivable consists of the following (amounts in thousands):
		December 31, 2014		March 31, 2014
	Trade accounts receivable	$	242,437	$	243,383
	Other	3,069		1,940
		245,506		245,323
	Less allowance for doubtful accounts	2,911		2,918
		$	242,595	$	242,405

Inventories_Tables

Inventories (Tables)	9 Months Ended
	Dec. 31, 2014
Inventory Disclosure [Abstract]
Components of inventories	The components of inventories consist of the following (amounts in thousands):
		December 31, 2014		March 31, 2014
	Raw materials	$	14,301	$	9,734
	Work in process	190,573		179,692
	Finished goods	71,269		73,299
		$	276,143	$	262,725

Property_Plant_and_Equipment_T

Property, Plant and Equipment (Tables)	9 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	Property, plant and equipment consists of the following (amounts in thousands):
		December 31, 2014		March 31, 2014
	Land	$	55,624	$	55,624
	Building and building improvements	430,695		411,149
	Machinery and equipment	1,549,999		1,465,255
	Projects in process	75,800		68,991
		2,112,118		2,001,019
	Less accumulated depreciation and amortization	1,534,995		1,469,052
		$	577,123	$	531,967

Noncontrolling_Interests_Table

Noncontrolling Interests (Tables)	9 Months Ended
	Dec. 31, 2014
Noncontrolling Interest [Abstract]
Schedule of changes in the components of noncontrolling interest	The following table presents the changes in the components of noncontrolling interests for the nine months ended December 31, 2014 (amounts in thousands):
		Noncontrolling Interests
	Balance at March 31, 2014	$	—
	Additions due to acquisition of controlling interest in ISSC	52,467
	Net loss attributable to noncontrolling interests	(2,862		)
	Other comprehensive loss attributable to noncontrolling interests	(866		)
	Purchase of additional interests	(23,054		)
	Other	304
	Balance at December 31, 2014	$	25,989
Schedule of changes in the Company's ownership interest in ISSC	The following table presents the effect of changes in the Company's ownership interest in ISSC on the Company's stockholders' equity for the nine months ended December 31, 2014 (amounts in thousands):
		Nine Months Ended
		31-Dec-14
	Net income attributable to Microchip Technology stockholders	$	269,607
	Increase in paid-in capital for purchase of additional interests	568
	Increase in paid-in capital for converted stock options	1,094
	Transfers from noncontrolling interest	1,662
	Change from net income attributable to Microchip Technology stockholders and transfers from noncontrolling interest	$	271,269

Intangible_Assets_and_Goodwill1

Intangible Assets and Goodwill (Tables)	9 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Intangible assets consist of the following (amounts in thousands):
			December 31, 2014
			Gross Amount			Accumulated Amortization			Net Amount
	Developed technology		$	563,272		$	(185,391	)	$	377,881
	Customer-related		263,969			(170,719		)	93,250
	Trademarks and trade names		15,730			(8,926		)	6,804
	Backlog		26,302			(25,818		)	484
	In-process technology		72,442			—			72,442
	Distribution rights		5,585			(5,236		)	349
	Covenants not to compete		400			(400		)	—
			$	947,700		$	(396,490	)	$	551,210
			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	$48,377
	2016	146,898
	2017	91,833
	2018	69,488
	2019	62,732
Goodwill Activity	Goodwill activity for the nine months ended December 31, 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	137,178			—
	Additions due to acquisition of controlling interest in ISSC	154,399			—
	Adjustments due to other acquisitions	625			—
	Foreign currency translation adjustments	(3,009		)	—
	Balance at December 31, 2014	$	546,090		$	19,200

Comprehensive_Income_Tables

Comprehensive Income (Tables)	9 Months Ended
	Dec. 31, 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 nine months ended December 31, 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 (loss) before reclassifications	19,439			—			(4,322		)		15,117
	Amounts reclassified from accumulated other comprehensive income (loss)	(157		)	—			—				(157		)
	Net other comprehensive income (loss)	19,282			—			(4,322		)		14,960
	Purchase of shares from noncontrolling interest	—			—			(448		)		(448		)
	Balance at December 31, 2014	$	18,754		$	140		$	(3,331	)		$	15,563
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						Nine Months Ended
			December 31,						December 31,
	Description of AOCI Component		2014			2013			2014				2013			Related Statement
																of Income Line
	Unrealized gains on available-for-sale securities		$	73		$	113		$	169			$	2,279		Other income
	Taxes		—			—			(12		)		(776		)	Provision for income taxes
	Reclassification of realized transactions, net of taxes		$	73		$	113		$	157			$	1,503		Net income

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	9 Months Ended
	Dec. 31, 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						Nine Months Ended
		December 31,						December 31,
		2014			2013			2014			2013
	Cost of sales	$	2,290	(1)	$	1,841	(1)	$	6,985	(1)	$	5,674	(1)
	Research and development	7,075			6,141			20,645			18,762
	Selling, general and administrative	5,454			5,737			15,783			16,939
	Pre-tax effect of share-based compensation	14,819			13,719			43,413			41,375
	Income tax benefit	3,632			1,510			6,885			4,501
	Net income effect of share-based compensation	$	11,187		$	12,209		$	36,528		$	36,874

Net_income_per_common_share_Ta

Net income per common share (Tables)	9 Months Ended
	Dec. 31, 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 attributable to Microchip Technology stockholders (in thousands, except per share amounts):
		Three Months Ended				Nine Months Ended
		December 31,				December 31,
		2014		2013		2014		2013
	Net income attributable to Microchip Technology	$	86,057	$	105,401	$	269,607	$	283,786
	Weighted average common shares outstanding	201,203		198,759		200,673		197,845
	Dilutive effect of stock options and RSUs	3,396		3,834		3,652		3,882
	Dilutive effect of convertible debt	18,888		16,496		20,108		14,216
	Weighted average common and potential common shares outstanding	223,487		219,089		224,433		215,943
	Basic net income per common share attributable to Microchip Technology stockholders	$	0.43	$	0.53	$	1.34	$	1.43
	Diluted net income per common share attributable to Microchip Technology stockholders	$	0.39	$	0.48	$	1.2	$	1.31

Basis_of_Presentation_Details

Basis of Presentation (Details)	Dec. 31, 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 $)	9 Months Ended		0 Months Ended	3 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Jul. 17, 2014	Dec. 31, 2014	Apr. 01, 2014
Business Acquisition [Line Items]
Amount of cash paid, net of cash and short-term investments acquired	$375,365,000	$0
ISSC Technologies Corporation [Member]
Business Acquisition [Line Items]
Percentage of interest acquired in acquisition			83.50%
Purchased price paid			267,600,000
Net deferred tax liability for future amortization expense of acquired intangible assets			25,100,000
Revenue of acquiree included in statement of income since the acquisition date	25,600,000			8,700,000
Net income (loss) of acquiree included in statement of income since the acquisition date	-18,200,000			-10,000,000
Reduction in net sales due to contractual change in distributor agreements	7,100,000
Noncontrolling Interest, Ownership Percentage by Parent	91.10%			91.10%
Supertex Inc.
Business Acquisition [Line Items]
Tendered offer price per share					$33
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					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	$53,000,000			$18,600,000

Business_Acquisitions_Schedule

Business Acquisitions Schedule of Preliminary Allocation of Purchase Price (Details) (USD $)	3 Months Ended	6 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Mar. 31, 2014	Sep. 30, 2014	Jun. 30, 2014
Business Acquisition [Line Items]
Goodwill	$565,290,000	$565,290,000	$276,097,000
ISSC Technologies Corporation [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	15,120,000	15,120,000		15,120,000
Short-term investments	27,063,000	27,063,000		27,063,000
Accounts receivable, net	8,792,000	8,792,000		8,792,000
Inventories	16,542,000	16,542,000		19,160,000
Prepaid expenses and other current assets	2,501,000	2,501,000		2,501,000
Property, plant and equipment, net	2,637,000	2,637,000		2,637,000
Goodwill	154,399,000	154,399,000		152,243,000
Purchased intangible assets	147,800,000	147,800,000		147,800,000
Other assets	1,370,000	1,370,000		1,370,000
Total assets acquired	376,224,000	376,224,000		376,686,000
Accounts payable	-9,860,000	-9,860,000		-9,860,000
Other current liabilities	-16,535,000	-16,535,000		-16,997,000
Long-term income tax payable	-4,402,000	-4,402,000		-4,402,000
Deferred tax liability	-25,126,000	-25,126,000		-25,126,000
Other long-term liabilities	-245,000	-245,000		-245,000
Total liabilities assumed	-56,168,000	-56,168,000		-56,630,000
Net assets acquired	320,056,000	320,056,000		320,056,000
Less: noncontrolling interest	-52,467,000	-52,467,000		-52,467,000
Net assets acquired	267,589,000	267,589,000		267,589,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract]
Inventories	-2,618,000
Goodwill	2,156,000
Total assets acquired	-462,000
Accrued liabilities	462,000
Total liabilities assumed	462,000
Supertex Inc.
Business Acquisition [Line Items]
Cash and cash equivalents	14,790,000	14,790,000			14,790,000
Short-term investments	140,984,000	140,984,000			140,984,000
Accounts receivable, net	7,047,000	7,047,000			7,047,000
Inventories	27,630,000	27,630,000			27,630,000
Prepaid expenses	1,493,000	1,493,000			1,493,000
Deferred tax assets	3,997,000	3,997,000			3,997,000
Other current assets	16,113,000	16,113,000			16,113,000
Property, plant and equipment, net	15,679,000	15,679,000			15,679,000
Goodwill	137,178,000	137,178,000			133,713,000
Purchased intangible assets	89,600,000	89,600,000			89,600,000
Other assets	325,000	325,000			325,000
Total assets acquired	454,836,000	454,836,000			451,371,000
Accounts payable	-8,481,000	-8,481,000			-8,481,000
Accrued liabilities	-19,370,000	-19,370,000			-19,345,000
Long-term income tax payable	-3,796,000	-3,796,000			-3,796,000
Deferred tax liability	-31,412,000	-31,412,000			-27,972,000
Total liabilities assumed	-63,059,000	-63,059,000			-59,594,000
Net assets acquired	391,777,000	391,777,000			391,777,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract]
Goodwill		3,465,000
Total assets acquired		3,465,000
Accrued liabilities		-25,000
Deferred tax liability		-3,440,000
Total liabilities assumed		($3,465,000)

Business_Acquisitions_Schedule1

Business Acquisitions (Schedule of Purchased Intangible Assets) (Details) (USD $)	0 Months Ended
In Thousands, unless otherwise specified	Jul. 17, 2014	Apr. 01, 2014
ISSC Technologies Corporation [Member]
Business Acquisition [Line Items]
Purchased Intangible Assets	$147,800
ISSC Technologies Corporation [Member] | Core/developed technology
Business Acquisition [Line Items]
Useful Life	10 years
Purchased Intangible Assets	68,900
ISSC Technologies Corporation [Member] | In-process technology
Business Acquisition [Line Items]
Useful Life	10 years
Purchased Intangible Assets	27,200
ISSC Technologies Corporation [Member] | Customer-related
Business Acquisition [Line Items]
Useful Life	3 years
Purchased Intangible Assets	51,100
ISSC Technologies Corporation [Member] | Backlog
Business Acquisition [Line Items]
Useful Life	1 year
Purchased Intangible Assets	600
Supertex Inc.
Business Acquisition [Line Items]
Purchased Intangible Assets		89,600
Supertex Inc. | Core/developed technology
Business Acquisition [Line Items]
Useful Life		10 years
Purchased Intangible Assets		68,900
Supertex Inc. | In-process technology
Business Acquisition [Line Items]
Useful Life		10 years
Purchased Intangible Assets		1,900
Supertex Inc. | Customer-related
Business Acquisition [Line Items]
Useful Life		2 years
Purchased Intangible Assets		17,700
Supertex Inc. | Backlog
Business Acquisition [Line Items]
Useful Life		1 year
Purchased Intangible Assets		$1,100

Business_Acquisitions_Schedule2

Business Acquisitions (Schedule of Proforma Information) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
ISSC Technologies Corporation [Member]
Business Acquisition [Line Items]
Net sales	$528,710	$497,585	$1,626,183	$1,490,776
Net income	86,683	97,470	265,412	260,386
Basic earnings per share	$0.43	$0.49	$1.32	$1.32
Diluted earnings per share	$0.39	$0.44	$1.18	$1.21
Supertex Inc.
Business Acquisition [Line Items]
Net sales	528,710	499,722	1,606,298	1,486,661
Net income	$87,392	$99,741	$291,288	$251,976
Basic earnings per share	$0.43	$0.50	$1.45	$1.27
Diluted earnings per share	$0.39	$0.46	$1.30	$1.17

Special_Charges_Details

Special Charges (Details) (Unusual or Infrequent Item [Member], USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Unusual or Infrequent Item [Member]
Unusual or Infrequent Item [Line Items]
Other Nonrecurring Expense	$1	$0.80	$2.10	$2.50

Segment_Information_Details

Segment Information (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Segment reporting information [Line Items]
Net sales	$528,710	$482,372	$1,603,829	$1,437,833
Gross Profit	301,959	282,720	915,932	838,157
Semiconductor products [Member]
Segment reporting information [Line Items]
Net sales	505,763	458,298	1,537,861	1,366,415
Gross Profit	279,012	258,646	849,964	766,739
Technology licensing [Member]
Segment reporting information [Line Items]
Net sales	22,947	24,074	65,968	71,418
Gross Profit	$22,947	$24,074	$65,968	$71,418

Summary_of_Available_for_Sale_

Summary of Available for Sale (Details) (USD $)	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2014
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	$1,742,210	$1,677,422
Available-for-sale, gross unrealized gains	34,428	3,462
Available-for-sale, gross unrealized losses	-3,295	-3,990
Available-for-sale, estimated fair value	1,773,343	1,676,894
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position, Less than Twelve Months	1,042,371	781,501
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position, Twelve Months or Longer	70,683	1,196
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position	1,113,054	782,697
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position, Less than 12 Months	-2,956	-3,989
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position, 12 Months or Longer	-339	-1
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position	-3,295	-3,990
Government agency bonds [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	736,615	684,451
Available-for-sale, gross unrealized gains	113	114
Available-for-sale, gross unrealized losses	-1,866	-3,171
Available-for-sale, estimated fair value	734,862	681,394
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position, Less than Twelve Months	568,466	522,159
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position, Twelve Months or Longer	64,695	0
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position	633,161	522,159
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position, Less than 12 Months	-1,561	-3,172
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position, 12 Months or Longer	-305	0
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position	-1,866	-3,172
Municipal bonds [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	45,140	41,622
Available-for-sale, gross unrealized gains	74	101
Available-for-sale, gross unrealized losses	-32	-14
Available-for-sale, estimated fair value	45,182	41,709
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position, Less than Twelve Months	13,533	2,625
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position, Twelve Months or Longer	0	1,196
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position	13,533	3,821
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position, Less than 12 Months	-32	-13
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position, 12 Months or Longer	0	-1
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position	-32	-14
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
Time Deposits [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	8,699
Available-for-sale, gross unrealized gains	0
Available-for-sale, gross unrealized losses	0
Available-for-sale, estimated fair value	8,699
Corporate bonds and debt [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	938,331	941,524
Available-for-sale, gross unrealized gains	927	3,247
Available-for-sale, gross unrealized losses	-1,397	-805
Available-for-sale, estimated fair value	937,861	943,966
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position, Less than Twelve Months	460,372	256,717
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position, Twelve Months or Longer	5,988	0
Fair Value of Available-for-sale Securities in a Continuous Unrealized Loss Position	466,360	256,717
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position, Less than 12 Months	-1,363	-804
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position, 12 Months or Longer	-34	0
Aggregate Loss, Available-for-sale Securities in a Continuous Unrealized Loss Position	-1,397	-804
Equity Securities [Member]
Summary of available-for-sale securities [Line Items]
Available-for-sale, adjusted cost	3,600
Available-for-sale, gross unrealized gains	33,314
Available-for-sale, gross unrealized losses	0
Available-for-sale, estimated fair value	$36,914

Investments_AFS_Details

Investments AFS (Details) (USD $)	Dec. 31, 2014	Mar. 31, 2014
Investments [Abstract]
Amount of short-term investments	$666,119,000	$878,182,000
Amount of long-term investments	1,107,224,000	798,712,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,113,054,000	782,697,000
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 $)	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2014
Schedule of available-for-sale securities, debt maturities [Line Items]
Available-for-sale, adjusted cost	$1,742,210	$1,677,422
Available-for-sale, gross unrealized gains	34,428	3,462
Available-for-sale, gross unrealized losses	-3,295	-3,990
Available-for-sale, estimated fair value	1,773,343	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	216,444
Available-for-sale, gross unrealized gains	258
Available-for-sale, gross unrealized losses	-9
Available-for-sale, estimated fair value	216,693
Due after one year and through five years [Member]
Schedule of available-for-sale securities, debt maturities [Line Items]
Available-for-sale, adjusted cost	1,428,901
Available-for-sale, gross unrealized gains	835
Available-for-sale, gross unrealized losses	-3,081
Available-for-sale, estimated fair value	1,426,655
Due after five years and through ten years [Member]
Schedule of available-for-sale securities, debt maturities [Line Items]
Available-for-sale, adjusted cost	77,250
Available-for-sale, gross unrealized gains	21
Available-for-sale, gross unrealized losses	-205
Available-for-sale, estimated fair value	77,066
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	1,732,420
Available-for-sale, gross unrealized gains	1,114
Available-for-sale, gross unrealized losses	-3,295
Available-for-sale, estimated fair value	$1,730,239

Measured_on_Recurring_Basis_De

Measured on Recurring Basis (Details) (USD $)	9 Months Ended
	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market mutual funds	51,677,000	$192,159,000
Marketable equity securities	36,914,000
Corporate bonds and debt	937,861,000	943,966,000
Time deposits (1)	8,699,000
Government agency bonds	734,862,000	681,394,000
Deposit accounts	404,662,000	274,444,000
Municipal bonds	45,182,000	41,709,000
Auction rate securities	9,825,000	9,825,000
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	456,339,000	466,603,000	375,100,000	528,334,000
Short-term investments	666,119,000	878,182,000
Long-term investments	1,107,224,000	798,712,000
Total assets measured at fair value	2,229,682,000	2,143,497,000
Insurance Sector Auction Rate Securities [Member]
Available-for-sale Securities, Other Disclosure Items [Abstract]
Value of auction rate securities for which recent auctions were unsuccessful	9,800,000
Auction Rate Securities Par Value	22,400,000
Insurance Sector Auction Rate Securities [Member] | Minimum [Member]
Available-for-sale Securities, Other Disclosure Items [Abstract]
Discount rate	2.00%
Liquidity risk premium (percentage)	9.10%
Anticipated liquidity horizon	7 years
Insurance Sector Auction Rate Securities [Member] | Maximum [Member]
Available-for-sale Securities, Other Disclosure Items [Abstract]
Discount rate	2.50%
Liquidity risk premium (percentage)	29.50%
Anticipated liquidity horizon	10 years
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market mutual funds	51,677,000	192,159,000
Marketable equity securities	36,914,000
Corporate bonds and debt	0	0
Time deposits (1)	0
Government agency bonds	0	0
Deposit accounts	0	0
Municipal bonds	0	0
Auction rate securities	0	0
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	51,677,000	192,159,000
Short-term investments	36,914,000	0
Long-term investments	0	0
Total assets measured at fair value	88,591,000	192,159,000
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market mutual funds	0	0
Marketable equity securities	0
Corporate bonds and debt	931,671,000	937,776,000
Time deposits (1)	8,699,000
Government agency bonds	734,862,000	681,394,000
Deposit accounts	404,662,000	274,444,000
Municipal bonds	45,182,000	41,709,000
Auction rate securities	0	0
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	404,662,000	274,444,000
Short-term investments	629,205,000	878,182,000
Long-term investments	1,091,209,000	782,697,000
Total assets measured at fair value	2,125,076,000	1,935,323,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market mutual funds	0	0
Marketable equity securities	0
Corporate bonds and debt	6,190,000	6,190,000
Time deposits (1)	0
Government agency bonds	0	0
Deposit accounts	0	0
Municipal bonds	0	0
Auction rate securities	9,825,000	9,825,000
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	0	0
Short-term investments	0	0
Long-term investments	16,015,000	16,015,000
Total assets measured at fair value	16,015,000	$16,015,000

Unobservable_Input_Reconciliat

Unobservable Input Reconciliation Assets (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014
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)

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 $)	Dec. 31, 2014	Mar. 31, 2014
In Millions, unless otherwise specified
Fair Value Disclosures [Abstract]
Fair value of junior subordinated convertible debentures based on observable market prices	$2,051	$2,138

Accounts_Receivable_Details

Accounts Receivable (Details) (USD $)	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	$245,506	$245,323
Less allowance for doubtful accounts	2,911	2,918
Accounts receivable, net	242,595	242,405
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	242,437	243,383
Other Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	$3,069	$1,940

Inventories_Details

Inventories (Details) (USD $)	Dec. 31, 2014	Mar. 31, 2014
In Thousands, unless otherwise specified
Inventory Disclosure [Abstract]
Raw materials	$14,301	$9,734
Work in process	190,573	179,692
Finished goods	71,269	73,299
Inventory, Net	$276,143	$262,725

Assets_Held_for_Sale_Details

Assets Held for Sale (Details) (Property, Plant and Equipment, Other Types [Member], USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Property, Plant and Equipment, Other Types [Member]
Long Lived Assets Held-for-sale [Line Items]
Assets Held-for-sale, Long Lived, Fair Value Disclosure	$14.30
Asset Held-for-Sale Estimated Selling Cost	$0.30

Property_Plant_and_Equipment_D

Property, Plant and Equipment (Details) (USD $)	3 Months Ended		9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2014
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$2,112,118,000		$2,112,118,000		$2,001,019,000
Accumulated depreciation	1,534,995,000		1,534,995,000		1,469,052,000
Property, plant and equipment, net	577,123,000		577,123,000		531,967,000
Depreciation expense	24,700,000	22,200,000	72,300,000	66,700,000
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	55,624,000		55,624,000		55,624,000
Buildings and building improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	430,695,000		430,695,000		411,149,000
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	1,549,999,000		1,549,999,000		1,465,255,000
Projects in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant, and equipment costs	$75,800,000		$75,800,000		$68,991,000

Noncontrolling_Interests_Nonco

Noncontrolling Interests Noncontrolling Interest Roll Forward (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Balance at March 31, 2014			$0
Additions due to acquisition of controlling interest in ISSC			52,467
Net loss attributable to noncontrolling interests	-1,259	0	-2,862	0
Other comprehensive loss attributable to noncontrolling interests	149	0	-866	0
Purchase of additional interests			-23,054
Other			304
Balance at December 31, 2014	$25,989		$25,989

Noncontrolling_Interests_Chang

Noncontrolling Interests Change in Parent Ownership (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net income attributable to Microchip Technology stockholders	$86,057	$105,401	$269,607	$283,786
Increase in paid-in capital for purchase of additional interests			448
Parent [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net income attributable to Microchip Technology stockholders			269,607
Increase in paid-in capital for purchase of additional interests			568
Increase in paid-in capital for converted stock options			1,094
Transfers from noncontrolling interest			1,662
Change from net income attributable to Microchip Technology stockholders and transfers from noncontrolling interest			$271,269

Intangible_Assets_by_Major_Cla

Intangible Assets, by Major Class (Details) (USD $)	3 Months Ended		9 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Apr. 01, 2014	Mar. 31, 2014
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount	$947,700,000		$947,700,000			$709,190,000
Accumulated Amortization	-396,490,000		-396,490,000			-263,691,000
Net Amount	551,210,000		551,210,000			445,499,000
In-process technology reaching technological feasibility and reclassified			20,700,000
Amortization of Intangible Assets	48,600,000	23,000,000	132,800,000	77,000,000
Impairment of Intangible Assets	1,305,000		1,861,000	350,000
Future Amortization Expense, Remainder of Fiscal Year	48,377,000		48,377,000
Future Amortization Expense, Year Two	146,898,000		146,898,000
Future Amortization Expense, Year Three	91,833,000		91,833,000
Future Amortization Expense, Year Four	69,488,000		69,488,000
Future Amortization Expense, Year Five	62,732,000		62,732,000
Developed technology [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount	563,272,000		563,272,000			402,669,000
Accumulated Amortization	-185,391,000		-185,391,000			-117,222,000
Net Amount	377,881,000		377,881,000			285,447,000
Customer-related [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount	263,969,000		263,969,000			195,800,000
Accumulated Amortization	-170,719,000		-170,719,000			-109,170,000
Net Amount	93,250,000		93,250,000			86,630,000
Trademarks and trade names [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount	15,730,000		15,730,000			15,730,000
Accumulated Amortization	-8,926,000		-8,926,000			-7,118,000
Net Amount	6,804,000		6,804,000			8,612,000
Backlog [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount	26,302,000		26,302,000			24,610,000
Accumulated Amortization	-25,818,000		-25,818,000			-24,610,000
Net Amount	484,000		484,000			0
In-process technology [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount	72,442,000		72,442,000			64,396,000
Accumulated Amortization	0		0			0
Net Amount	72,442,000		72,442,000			64,396,000
Distribution rights [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount	5,585,000		5,585,000			5,585,000
Accumulated Amortization	-5,236,000		-5,236,000			-5,171,000
Net Amount	349,000		349,000			414,000
Covenants not to compete [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount	400,000		400,000			400,000
Accumulated Amortization	-400,000		-400,000			-400,000
Net Amount	0		0			0
Minimum [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Useful Life			1 year
Minimum expected useful life of finite lived intangible assets (in years)			1 year
Maximum [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Useful Life			15 years
Minimum expected useful life of finite lived intangible assets (in years)			15 years
Supertex Inc. [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Purchased Intangible Assets					89,600,000
Supertex Inc. [Member] | Developed technology [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Purchased Intangible Assets					68,900,000
Useful Life					10 years
Minimum expected useful life of finite lived intangible assets (in years)					10 years
Supertex Inc. [Member] | Backlog [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Purchased Intangible Assets					1,100,000
Useful Life					1 year
Minimum expected useful life of finite lived intangible assets (in years)					1 year
Cost of Sales [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Amortization of Intangible Assets	900,000	1,200,000	2,900,000	3,700,000
Operating Expense [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Amortization of Intangible Assets	$47,700,000	$21,800,000	$129,900,000	$73,300,000

Goodwill_by_Reporting_Segment_

Goodwill by Reporting Segment (Details) (USD $)	9 Months Ended
	Dec. 31, 2014	Mar. 31, 2014	Jun. 30, 2014	Sep. 30, 2014
Goodwill [Roll Forward]
Goodwill, beginning balance		$276,097,000
Goodwill, ending balance	565,290,000	276,097,000
Supertex Inc. [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance			133,713,000
Goodwill, ending balance	137,178,000		133,713,000
ISSC Technologies Corporation [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance				152,243,000
Goodwill, ending balance	154,399,000			152,243,000
Semiconductor products [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance		256,897,000
Goodwill, ending balance	546,090,000	256,897,000
Semiconductor products [Member] | Supertex Inc. [Member]
Goodwill [Roll Forward]
Additions due to business combination	137,178,000
Semiconductor products [Member] | ISSC Technologies Corporation [Member]
Goodwill [Roll Forward]
Additions due to business combination	154,399,000
Goodwill, Translation Adjustments	-3,009,000
Semiconductor products [Member] | Other acquisitions
Goodwill [Roll Forward]
Additions due to business combination	625,000
Technology licensing [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance		19,200,000
Goodwill, ending balance	19,200,000	19,200,000
Technology licensing [Member] | Supertex Inc. [Member]
Goodwill [Roll Forward]
Additions due to business combination	0
Technology licensing [Member] | ISSC Technologies Corporation [Member]
Goodwill [Roll Forward]
Additions due to business combination	0
Goodwill, Translation Adjustments	0
Technology licensing [Member] | Other acquisitions
Goodwill [Roll Forward]
Additions due to business combination	$0

Income_tax_Details

Income tax (Details) (USD $)	3 Months Ended	9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Effective Income Tax Rate		6.00%	9.70%
Release of prior year tax provisions	$1.90	$9.30
Release of prior year tax provisions basic earnings per share impact	$0.01	$0.04
Release of prior year tax provisions diluted earnings per share impact	$0.01	$0.04
Unrecognized Tax Benefits	222	222
Unrecognized Tax Benefits, Period Increase (Decrease)		42
Unrecognized tax benefit presented as a reduction to deferred tax assets for net operating loss carryforward and other tax credit carryforwards	$83.60	$83.60

2125_Junior_subordinated_conve1

2.125% Junior subordinated convertible debentures (Details) (USD $)	3 Months Ended	9 Months Ended		3 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2013	Mar. 31, 2014
Debt Instrument [Line Items]
Carrying value of debentures	$379,263,000	$379,263,000			$371,873,000
Amortization of Debt Discount (Premium)	2,500,000	7,311,000	6,682,000
Junior subordinated convertible debentures due 2037 [Member]
Debt Instrument [Line Items]
Principal amount of junior subordinated convertible debentures	1,150,000,000	1,150,000,000
Interest rate of junior subordinated convertible debentures	2.13%	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	$34.16
Debt Instrument, Convertible, Conversion Ratio		39.5749
Debt Instrument, Convertible, Conversion Price	$25.27	$25.27
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			822,400,000
Estimated fair value of liability component of debentures at issuance date	327,600,000	327,600,000
Debt discount of estimated fair value of liability component of debentures	822,400,000	822,400,000
Amount of unamortized debt discount of debentures	769,900,000	769,900,000			777,200,000
Remaining period, in years, over which unamortized debt discount will be recognized as non-cash interest expense (in years)		23 years
Amortization of Debt Discount (Premium)				2,300,000
Recognized amount of interest expense related to debentures	$6,100,000	$18,300,000		$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	$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	$150

Credit_facility_Details

Credit facility (Details) (USD $)	3 Months Ended		9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Jun. 27, 2013
Line of Credit Facility [Line Items]
Interest expense	$14,223,000	$12,545,000	$41,920,000	$36,755,000
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	981,300,000		981,300,000
Debt discount	1,000,000		1,000,000
Interest expense	5,300,000	4,100,000	15,400,000	11,500,000
Short-term Debt, Weighted Average Interest Rate	1.67%		1.67%
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	336,900,000		336,900,000
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	644,400,000		644,400,000
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) (Indemnification Agreement [Member], USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Indemnification Agreement [Member]
Loss Contingencies [Line Items]
Loss contingencies, estimate of possible loss	$138

Derivative_Instruments_Details

Derivative Instruments (Details)	9 Months Ended
	Dec. 31, 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		9 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Changes in the components of AOCI
Balance at March 31, 2014			$1,051
Other comprehensive income (loss) before reclassifications			15,117
Amounts reclassified from accumulated other comprehensive income (loss)			-157
Other comprehensive income (loss) attributable to Microchip Technology	20,668	-54	14,960	-9,514
Purchase of shares from noncontrolling interest			448
Balance at December 31, 2014	15,563		15,563
Unrealized holding gains (losses) on available-for-sale securities
Changes in the components of AOCI
Balance at March 31, 2014			-528
Other comprehensive income (loss) before reclassifications			19,439
Amounts reclassified from accumulated other comprehensive income (loss)			-157
Other comprehensive income (loss) attributable to Microchip Technology			19,282
Balance at December 31, 2014	18,754		18,754
Minimum pension liability
Changes in the components of AOCI
Balance at March 31, 2014			140
Other comprehensive income (loss) before reclassifications			0
Amounts reclassified from accumulated other comprehensive income (loss)			0
Other comprehensive income (loss) attributable to Microchip Technology			0
Balance at December 31, 2014	140		140
Foreign Currency
Changes in the components of AOCI
Balance at March 31, 2014			1,439
Other comprehensive income (loss) before reclassifications			-4,322
Amounts reclassified from accumulated other comprehensive income (loss)			0
Other comprehensive income (loss) attributable to Microchip Technology			-4,322
Purchase of shares from noncontrolling interest			-448
Balance at December 31, 2014	($3,331)		($3,331)

Comprehensive_Income_Schedule_1

Comprehensive Income (Schedule of Reclassifications of Recognized Transactions out of AOCI) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Nonoperating Income (Expense)	($2,457)	$3,824	($3,535)	$6,093
Income Tax Expense (Benefit)	-1,393	-7,187	-17,141	-30,344
Net income attributable to Microchip Technology	86,057	105,401	269,607	283,786
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)	73	113	169	2,279
Income Tax Expense (Benefit)	0	0	-12	-776
Net income attributable to Microchip Technology	$73	$113	$157	$1,503

ShareBased_Compensation_Detail

Share-Based Compensation (Details) (USD $)	3 Months Ended				9 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2014		Dec. 31, 2013
Stock-based compensation expense [Line Items]
Allocated Share-based Compensation Expense	$11,187,000		$12,209,000		$36,528,000		$36,874,000
Inventory [Member]
Stock-based compensation expense [Line Items]
Amount of share-based compensation expense capitalized to inventory	1,700,000		1,900,000		5,000,000		5,700,000
Cost of Sales [Member]
Stock-based compensation expense [Line Items]
Allocated Share-based Compensation Expense	2,290,000	[1]	1,841,000	[1]	6,985,000	[1]	5,674,000	[1]
Research and development [Member]
Stock-based compensation expense [Line Items]
Allocated Share-based Compensation Expense	7,075,000		6,141,000		20,645,000		18,762,000
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense [Line Items]
Allocated Share-based Compensation Expense	5,454,000		5,737,000		15,783,000		16,939,000
Pre-tax effect of share based compensation [Member]
Stock-based compensation expense [Line Items]
Allocated Share-based Compensation Expense	14,819,000		13,719,000		43,413,000		41,375,000
Income tax benefit [Member]
Stock-based compensation expense [Line Items]
Allocated Share-based Compensation Expense	$3,632,000		$1,510,000		$6,885,000		$4,501,000
[1]	During the three and nine months ended DecemberB 31, 2014, $1.7 million and $5.0 million, respectively, of share-based compensation expense was capitalized to inventory and $2.3 million and $7.0 million, respectively, of previously capitalized share-based compensation expense in inventory was sold. During the three and nine months ended DecemberB 31, 2013, $1.9 million and $5.7 million, respectively, of share-based compensation expense was capitalized to inventory and $1.8 million and $5.7 million, respectively, 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		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income attributable to Microchip Technology	$86,057	$105,401	$269,607	$283,786
Weighted average common shares outstanding	201,203,000	198,759,000	200,673,000	197,845,000
Dilutive effect of stock options and RSUs	3,396,000	3,834,000	3,652,000	3,882,000
Dilutive effect of convertible debt	18,888,013	16,496,384	20,107,818	14,215,573
Weighted average common and potential common shares outstanding	223,487,000	219,089,000	224,433,000	215,943,000
Basic net income per common share attributable to Microchip Technology stockholders	$0.43	$0.53	$1.34	$1.43
Diluted net income per common share attributable to Microchip Technology stockholders	$0.39	$0.48	$1.20	$1.31
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (amount per share)	$25.39	$26.19	$25.57	$26.43
Number of antidilutive option shares (in shares)	46,959	0	46,959	0

Dividends_Details

Dividends (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended		0 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 05, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Jan. 29, 2015
Dividends [Abstract]
Dividend per share paid during period	$0.36			$1.07
Cash Dividend	$71.80			$214.40
Subsequent Event [Line Items]
Dividends declared per common share		$0.36	$0.35	$1.07	$1.06
Total amount of expected dividend payment	71.8			214.4
Subsequent Event [Member]
Dividends [Abstract]
Cash Dividend						72
Subsequent Event [Line Items]
Dividends declared per common share						$0.36
Total amount of expected dividend payment						$72