Significant Accounting Policies (Policies)	12 Months Ended
Significant Accounting Policies (Policies)	Mar. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The Company prepares its consolidated financial statements in accordance with generally accepted accounting principles in the United States of America (US GAAP). The consolidated financial statements include the accounts of Microchip and its majority-owned and controlled subsidiaries. All of the Company's subsidiaries are included in the consolidated financial statements. All significant intercompany accounts and transactions have been eliminated in consolidation.
Revenue Recognition	Revenue Recognition (prior to the adoption of ASC 606) The Company recognizes revenue when the earnings process is complete, as evidenced by an agreement with the customer, transfer of title has occurred, the pricing is fixed or determinable and collectability is reasonably assured. The Company recognizes revenue from product sales to original equipment manufacturers (OEMs) upon shipment and records reserves for estimated customer returns. Distributors worldwide generally have broad price protection and product return rights which prevent the sales pricing from being fixed or determinable at the time of the Company's shipment to the distributors. Therefore, revenue recognition is deferred until the pricing uncertainty is resolved, which generally occurs when the distributor sells the product to their customer. At the time of shipment to these distributors, the Company records a trade receivable for the selling price as there is a legally enforceable right to payment, relieves inventory for the carrying value of goods shipped since legal title has passed to the distributor, and records the gross margin in deferred income on shipments to distributors on its consolidated balance sheets. In connection with its acquisitions of Atmel and Micrel, the Company acquired certain distributor relationships where revenue was recognized upon shipment to the distributors based on certain contractual terms or prevailing business practices that resulted in the price being fixed and determinable at such time. Following an acquisition, the Company undertakes efforts to align the contract terms and business practices of the acquired entity with its own. Once these efforts are complete, the related revenue recognition is changed. With respect to such distributor relationships acquired in the Atmel acquisition, as of October 1, 2016, these business practices were conformed to those of the Company’s other distributors, which beginning in October 2016 resulted in the deferral of revenue recognition until the distributor sells the product to their customers. With respect to such distributor relationships acquired in the Micrel acquisition, in the December 2015 quarter, these distributor contracts were changed to be consistent with those of the Company’s other distributors which resulted in the deferral of revenue recognition under such contracts until the distributor sells the product to their customers. Deferred income on shipments to distributors effectively represents gross margin on the sale to the distributor at the initial shipment date; however, the amount of gross margin recognized by the Company in future periods will be less than the deferred margin as a result of credits granted to distributors on specifically identified products and customers to allow the distributors to earn a competitive gross margin on the sale of the Company's products to their end customers and price protection concessions related to market pricing conditions. The Company sells the majority of the items in its product catalog to its distributors worldwide at a uniform list price. However, distributors resell the Company's products to end customers at a broad range of individually negotiated price points. The majority of the Company's distributors' resales require a reduction from the original list price paid. Often, under these circumstances, the Company remits back to the distributor a portion of their original purchase price after the resale transaction is completed in the form of a credit against the distributors' outstanding accounts receivable balance. The credits are on a per unit basis and are not given to the distributor until they provide information regarding the sale to their end customer. The price reductions vary significantly based on the customer, product, quantity ordered, geographic location and other factors and discounts to a price less than the Company's cost have historically been rare. The effect of granting these credits establishes the net selling price from the Company to its distributors for the product and results in the net revenue recognized by the Company when the product is sold by the distributors to their end customers. Thus, a portion of the "deferred income on shipments to distributors" balance represents the amount of distributors' original purchase price that will be credited back to the distributors in the future. The Company does not reduce deferred income on shipments to distributors or accounts receivable by anticipated future price concessions; rather, price concessions are recorded against deferred income on shipments to distributors when incurred, which is generally at the time the distributor sells the product. At March 31, 2018, the Company had approximately $479.6 million of deferred revenue and $145.8 million in deferred cost of sales recognized as $333.8 million of deferred income on shipments to distributors. At March 31, 2017, the Company had approximately $418.0 million of deferred revenue and $125.2 million in deferred cost of sales recognized as $292.8 million of deferred income on shipments to distributors. The deferred income on shipments to distributors that will ultimately be recognized in the Company's income statement will be lower than the amount reflected on the balance sheet due to price credits to be granted to the distributors when the product is sold to their customers. These price credits historically have resulted in the deferred income approximating the overall gross margins that the Company recognizes in the distribution channel of its business. The Company reduces product pricing through price protection based on market conditions, competitive considerations and other factors. Price protection is granted to distributors on the inventory they have on hand at the date the price protection is offered. When the Company reduces the price of its products, it allows the distributor to claim a credit against its outstanding accounts receivable balances based on the new price of the inventory it has on hand as of the date of the price reduction. There is no immediate revenue impact from the price protection, as it is reflected as a reduction of the deferred income on shipments to distributors' balance. Products returned by distributors and subsequently scrapped have historically been immaterial to the Company's consolidated results of operations. The Company routinely evaluates the risk of impairment of the deferred cost of sales component of the deferred income on shipments to distributors' account. Because of the historically immaterial amounts of inventory that have been scrapped, and historically rare instances where discounts given to a distributor result in a price less than the Company's cost, the Company believes the deferred costs have a low risk of material impairment. Shipping charges billed to customers are included in net sales, and the related shipping costs are included in cost of sales. The Company collects and remits certain sales-related taxes on a portion of its sales of inventory and reports such amounts under the net method in its consolidated statements of income. For licenses or other technology arrangements without an upgrade period, non-royalty revenue from the license is recognized upon delivery of the technology if the fee is fixed or determinable and collection of the fee is reasonably assured. Royalties are recognized when reported to the Company, which generally coincides with the receipt of payment. In certain limited circumstances, the Company enters into license and other arrangements for technologies that the Company is continuing to enhance and refine or under which it is obligated to provide unspecified enhancements. Under these arrangements, non-royalty revenue is recognized over the lesser of (1) the estimated period that the Company has historically enhanced and developed refinements to the specific technology, typically one to three years (the "upgrade period"), and (2) the remaining portion of the upgrade period after the date of delivery of all specified technology and documentation, provided that the fee is fixed or determinable and collection of the fee is reasonably assured. Royalties received during the upgrade period are recognized as revenue based on an amortization calculation of the elapsed portion of the upgrade period compared to the entire estimated upgrade period. Royalties received after the upgrade period has elapsed are recognized when reported to the Company, which generally coincides with the receipt of payment. Changes to Revenue Recognition Resulting From the Adoption of ASC 606 In May 2014, the Financial Accounting Standards Board (FASB) issued ASU 2014-09-Revenue from Contracts with Customers (Topic 606), which superseded nearly all existing revenue recognition guidance under generally accepted accounting principles in the United States of America (US GAAP). In August 2015, the FASB issued ASU 2015-14-Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which delayed the effective date of the new standard by one year to December 15, 2017, for annual and interim reporting periods beginning after that date. In accordance with the delay, the new standard was effective for the Company beginning April 1, 2018. 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 new standard allows for the amendment to be applied either retrospectively to each prior reporting period presented or retrospectively as a cumulative-effect adjustment as of the date of adoption. In March 2016, the FASB issued ASU 2016-08-Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net), which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10-Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies the implementation guidance on identifying performance obligations. In May 2016, the FASB issued ASU 2016-12-Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, which addresses implementation issues that were raised by stakeholders and discussed by the Revenue Recognition Transition Resource Group. For a discussion of the financial statement impact related to the adoption of these standards, see “Recently Issued Accounting Pronouncements Not Yet Adopted”.
Product Warranty	Product Warranty The Company typically warrants its products against defects in materials and workmanship and non-conformance to specifications for 12 to 24 months. The majority of the Company's product warranty claims are settled through the return of the defective product and the shipment of replacement product. Warranty returns are included within the Company's allowance for returns, which is based on historical return rates. Actual future returns could differ from the allowance established. In addition, the Company accrues a liability for specific warranty costs expected to be settled other than through product return and replacement, if a loss is probable and can be reasonably estimated. Product warranty expenses were immaterial for the fiscal years ended March 31, 2018, 2017, and 2016.
Advertising Costs	Advertising Costs The Company expenses all advertising costs as incurred.
Research and Development	Research and Development Research and development costs are expensed as incurred. Assets purchased to support the Company's ongoing research and development activities are capitalized when related to products which have achieved technological feasibility or that have alternative future uses and are amortized over their estimated useful lives. Renewals or extensions of these assets are expensed as incurred. Research and development expenses include expenditures for labor, share-based payments, depreciation, masks, prototype wafers, and expenses for development of process technologies, new packages, and software to support new products and design environments.
Restructuring Charges	Restructuring Charges The Company recognizes a liability measured at fair value for restructuring costs when the liability is incurred. Restructuring charges are included within special charges and other, net in the consolidated statements of income and are primarily comprised of employee separation costs, asset impairments, contract exit costs and costs of facility consolidation and closure, including the related gains or losses associated with the sale of owned facilities. Employee separation costs includes one-time termination benefits that are recognized as a liability at estimated fair value, at the time of communication to employees, unless future service is required, in which case the costs are recognized ratably over the future service period. Ongoing termination benefits are recognized as a liability at estimated fair value when the amount of such benefits are probable and reasonably estimable. Contract exit costs includes contract termination fees and future contractual commitments for lease payments. A liability for contract exit costs is recognized in the period in which the Company terminates the contract or on the cease-use date for leased facilities.
Foreign Currency Translation	Foreign Currency Translation The Company's foreign subsidiaries are considered to be extensions of the U.S. company and any translation gains and losses related to these subsidiaries are included in other income (expense) in the consolidated statements of income. As the U.S. dollar is utilized as the functional currency, gains and losses resulting from foreign currency transactions (transactions denominated in a currency other than the subsidiaries' functional currency) are also included in income. For a portion of fiscal 2017, certain foreign subsidiaries acquired as part of the Company's acquisition activities had the local currency as the functional currency. Once these entities were integrated into the Company's legal structure and intercompany agreements were executed, the U.S. dollar became the functional currency for such entities.
Income Taxes	Income Taxes As part of the process of preparing its consolidated financial statements, the Company is required to estimate its income taxes in each of the jurisdictions in which it operates. This process involves estimating its actual current tax exposure together with assessing temporary differences resulting from differing treatment of items for tax and accounting purposes. These differences result in deferred tax assets and liabilities, which are included within the Company's consolidated balance sheets. The Company must then assess the likelihood that its deferred tax assets will be recovered from future taxable income within the relevant jurisdiction and to the extent the Company believes that recovery is not likely, it must establish a valuation allowance. The Company provided valuation allowances for certain of its deferred tax assets, including state net operating loss carryforwards and state tax credits, where it is more likely than not that some portion, or all of such assets, will not be realized. Due to the Tax Cuts and Jobs Act (the "Act"), the Company released its valuation allowance on foreign tax credits during the period ending March 31, 2018, which was provisional. The Company is still evaluating how the Act impacts its valuation allowance on state net operating loss carryforwards and state tax credits, and it may report an adjustment to the valuation allowances under Staff Accounting Bulletin ("SAB") 118 in subsequent quarters. Should the Company determine that it would not be able to realize all or part of its net deferred tax asset in the future, an adjustment to the deferred tax asset would be charged to income in the period such determination was made. Various taxing authorities in the U.S. and other countries in which the Company does business scrutinize the tax structures employed by businesses. Companies of a similar size and complexity as the Company are regularly audited by the taxing authorities in the jurisdictions in which they conduct significant operations. During the year ended March 31, 2018, various foreign jurisdictions finalized their audits. The close of these audits did not have an adverse impact on our financial statements. The Company is currently being audited by the tax authorities in the United States and various foreign jurisdictions. At this time, the Company does not know what the outcome of these audits will be. We record benefits for uncertain tax positions based on an assessment of whether it is more likely than not that the tax positions will be sustained based on their technical merits under currently enacted law. If this threshold is not met, no tax benefit of the uncertain tax position is recognized. If the threshold is met, we recognize the largest amount of the tax benefit that is more than 50% likely to be realized upon ultimate settlement. The accounting model as defined in Accounting Standards Codification ("ASC") 740 related to the valuation of uncertain tax positions requires the Company to presume that the tax position will be examined by the relevant taxing authority that has full knowledge of all relevant information and that each tax position will be evaluated without consideration of the possibility of offset or aggregation with other positions. The recognition requirement for the liability exists even if the Company believes the possibility of examination by a taxing authority or discovery of the related risk matters is remote or where it has a long history of the taxing authority not performing an exam or overlooking an issue. The Company will record an adjustment to a previously recorded position if new information or facts related to the position are identified in a subsequent period. All adjustments to the positions are recorded through the income statement. Generally, adjustments will be recorded in periods subsequent to the initial recognition if the taxing authority has completed an audit of the period or if the statute of limitation expires. Due to the inherent uncertainty in the estimation process and in consideration of the criteria of the accounting model, amounts recognized in the financial statements in periods subsequent to the initial recognition may significantly differ from the estimated exposure of the position under the accounting model. On December 22, 2017, the Act was enacted into law. The Act provides for numerous significant tax law changes and modifications including the reduction of the U.S. federal corporate income tax rate from 35.0% to 21.0%, the requirement for companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and the creation of new taxes on certain foreign-sourced earnings. As a fiscal year-end taxpayer, certain provisions of the Act began to impact the Company in the third quarter of fiscal 2018, while other provisions will impact the Company beginning in fiscal 2019. The corporate tax rate reduction is effective as of January 1, 2018. Since the Company has a fiscal year rather than a calendar year, it is subject to rules relating to transitional tax rates. As a result, the Company's fiscal 2018 federal statutory rate will be a blended rate of 31.5%. In addition to the impacts of tax reform on fiscal 2018, the Act establishes new tax laws that will be effective for fiscal 2019, including, but not limited to, (1) a new provision designed to tax low-taxed income of foreign subsidiaries, which allows for the possibility of using foreign tax credits ("FTCs") and a deduction of up to 50% to offset the income tax liability (subject to some limitations); (2) limitations on the deductibility of certain executive compensation; (3) limitations on the deductibility of interest expense; and (4) limitations on the use of FTCs to reduce the U.S. income tax liability. While each of these provisions is expected to have an impact on the Company's tax expense for fiscal 2019 and future periods, the Company expects the tax on low-taxed income of foreign subsidiaries to have the most significant, adverse impact on its results. Due to the complexity of the new tax on low-taxed income of foreign subsidiaries, the Company is continuing to evaluate this provision of the Act and the application of ASC 740. Based on recent FASB deliberations, it appears the Company will be allowed to make an accounting policy choice of either (1) treating taxes due on future U.S. inclusions in taxable income as a current-period expense when incurred or (2) factoring such amounts into its measurement of deferred taxes. The Company's selection of an accounting policy will depend, in part, on analyzing its facts to determine what the impact is expected to be under each method.
Cash and Cash Equivalents	Cash and Cash Equivalents All highly liquid investments, including marketable securities with an original maturity to the Company of three months or less when acquired are considered to be cash equivalents.
Available-for-Sale Investments	Available-for-Sale Investments The Company classifies its investments in debt and marketable equity securities as available-for-sale based upon management's intent with regard to the investments and the nature of the underlying securities. The Company's available-for-sale investments consist of government agency bonds, municipal bonds, corporate bonds and marketable equity securities. The Company's investments are carried at fair value with unrealized gains and losses reported in stockholders' equity unless losses are considered to be other than temporary impairments in which case the losses are recognized through the statement of income. Premiums and discounts are amortized or accreted over the life of the related available-for-sale security. Dividend and interest income are recognized when earned. The cost of available-for-sale debt securities sold is calculated using the first-in, first-out (FIFO) basis at the individual security level for sales from multiple lots. For sales of marketable equity securities, the Company uses an average cost basis at the individual security level. The Company includes within short-term investments its income yielding available-for-sale securities that can be readily converted to cash and includes within long-term investments those income yielding available-for-sale securities with maturities of over one year that have unrealized losses attributable to them or those that cannot be readily liquidated. As discussed in Note 4, if the Company anticipates that investments will be liquidated in anticipation of a pending merger, any unrealized losses are recognized as other-than-temporary impairments. If the anticipated liquidity event is within 12 months, the securities are classified as short-term investments. In the normal course of business, the Company intends and has the ability to hold its long-term investments with temporary impairments until such time as these assets are no longer impaired. As of March 31, 2018, such recovery of unrealized losses is not expected to occur within the next year as the investments will be sold.
Derivative Instruments	Derivative Instruments Derivative instruments are required to be recorded at fair value as either assets or liabilities in the Company's consolidated balance sheet. The Company's accounting policies for derivative instruments depends on whether the instrument has been designated and qualifies as part of a hedging relationship and further, on the type of hedging relationship. The Company does not apply hedge accounting to foreign currency forward contracts. Gains and losses associated with currency rate changes on forward contracts are recorded currently in income. These gains and losses have been immaterial to the Company's financial statements. The Company is exposed to fluctuations in prices for energy that it consumes, particularly electricity and natural gas. The Company also enters into variable-priced contracts for some purchases of electricity and natural gas, on an index basis. The Company seeks, or may seek, to partially mitigate these exposures through fixed-price contracts. These contracts meet the characteristics of derivative instruments, but generally qualify for the “normal purchases or normal sales” exception under authoritative guidance and require no mark-to-market adjustment. Interest rate derivative instruments designated as fair value hedges are designed to manage the exposure to interest rate movements and to reduce borrowing costs by converting fixed-rate debt into floating-rate debt. Under these agreements, the Company agrees to exchange, at specified intervals, the difference between the fixed and floating interest amounts calculated by reference to an agreed-upon notional principal amount. For derivative instruments that are designated and qualify as fair value hedges, the gain or loss on the derivatives as well as the offsetting gain or loss on the hedged item attributable to the hedged risk are recognized in earnings. The Company evaluates hedge effectiveness at inception and on an ongoing basis. If a derivative is no longer expected to be highly effective, hedge accounting is discontinued.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts The Company maintains an allowance for doubtful accounts for probable losses on uncollectible accounts receivable resulting from the inability of its customers to make required payments, which is included in bad debt expense. The Company determines the adequacy of this allowance by routinely analyzing the composition of accounts receivable and evaluating customer creditworthiness, credit history, facts and circumstances specific to outstanding balances and current economic conditions.
Inventories	Inventories Inventories are valued at the lower of cost or net realizable value using the first-in, first-out method. The Company writes down its inventory for estimated obsolescence or unmarketable inventory in an amount equal to the difference between the cost of inventory and the estimated net realizable value based upon assumptions about future demand and market conditions. If actual market conditions are less favorable than those projected by the Company, additional inventory write-downs may be required. 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. In estimating reserves for obsolescence, the Company primarily evaluates estimates of demand over a 12-month period and provides reserves for inventory on hand in excess of the estimated 12-month demand. Estimates for projected 12-month demand are generally based on the average shipments of the prior three-month period, which are then annualized to adjust for any potential seasonality in the Company's business. The estimated 12-month demand is compared to the Company's most recently developed sales forecast to further reconcile the 12-month demand estimate. Management reviews and adjusts the estimates as appropriate based on specific situations. For example, demand can be adjusted up for new products for which historic sales are not representative of future demand. Alternatively, demand can be adjusted down to the extent any existing products are being replaced or discontinued. In periods where the Company's production levels are substantially below normal operating capacity, unabsorbed overhead production costs associated with the reduced production levels of the Company's manufacturing facilities are charged directly to cost of sales.
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment are stated at cost. Major renewals and improvements are capitalized, while maintenance and repairs are expensed when incurred. The Company's property and equipment accounting policies incorporate estimates, assumptions and judgments relative to the useful lives of its property and equipment. Depreciation is provided for assets placed in service on a straight-line basis over the estimated useful lives of the relative assets, which range from 10 to 40 years for buildings and building improvements and 3 to 7 years for machinery and equipment. The Company evaluates the carrying value of its property and equipment when events or changes in circumstances indicate that the carrying value of such assets may be impaired. Asset impairment evaluations are, by nature, highly subjective.
Senior and Junior Subordinated Convertible Debt	Senior and Junior Subordinated Convertible Debt The Company separately accounts for the liability and equity components of its senior and junior subordinated convertible debt in a manner that reflects its nonconvertible debt (unsecured debt) borrowing rate when interest cost is recognized. This results in a bifurcation of a component of the debt, classification of that component in equity and the accretion of the resulting discount on the debt to be recognized as part of interest expense in its consolidated statements of income. Lastly, the Company includes the dilutive effect of the shares of its common stock issuable upon conversion of the outstanding senior and junior subordinated convertible debt in its diluted income per share calculation regardless of whether the market price triggers or other contingent conversion features have been met. The Company applies the treasury stock method as it has the intent and ability to settle the principal amounts of the senior and junior subordinated convertible debentures in cash. This method results in incremental dilutive shares when the average market value of the Company's common stock for a reporting period exceeds the conversion prices per share and adjust as dividends are recorded in the future. Upon a de-recognition event such as a settlement or conversion, the Company estimates the fair value of the liability component and compares that to the carrying amount in order to calculate the appropriate amount of gain or loss. The remaining amounts paid or issued (in the case of non cash consideration in the form of shares of common stock) are recognized as a reduction of additional paid-in-capital. The fair value of the liability component is estimated using the current comparable borrowing rate for an otherwise identical non-convertible debt instrument.
Defined Benefit Pension Plans	Defined Benefit Pension Plans The Company maintains defined benefit pension plans, covering certain of its foreign employees. For financial reporting purposes, net periodic pension costs and pension obligations are determined based upon a number of actuarial assumptions, including discount rates for plan obligations, and assumed rates of compensation increases for employees participating in plans. These assumptions are based upon management's judgment and consultation with actuaries, considering all known trends and uncertainties.
Contingencies	Contingencies In the ordinary course of business, the Company is exposed to various liabilities as a result of contracts, product liability, customer claims and other matters. Additionally, the Company is involved in a limited number of legal actions, both as plaintiff and defendant. Consequently, the Company could incur uninsured liability in any of those actions. The Company also periodically receives notifications from various third parties alleging infringement of patents or other intellectual property rights, or from customers requesting reimbursement for various costs. With respect to pending legal actions to which the Company is a party and other claims, although the outcomes are generally not 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 and disputes relating to the semiconductor industry are not uncommon, and the Company is, from time to time, subject to such litigation and disputes. As a result, no assurances can be given with respect to the extent or outcome of any such litigation or disputes in the future. The Company accrues for claims and contingencies when losses become probable and reasonably estimable. As of the end of each applicable reporting period, the Company reviews each of its matters and, where it is probable that a liability has been or will be incurred, it accrues for all probable and reasonably estimable losses. Where the Company can reasonably estimate a range of losses it may incur regarding such a matter, it records an accrual for the amount within the range that constitutes its best estimate. If the Company can reasonably estimate a range but no amount within the range appears to be a better estimate than any other, it uses the amount that is the low end of such range.
Business Combinations	Business Combinations All of the Company's business combinations are accounted for at fair value under the acquisition method of accounting. Under the acquisition method of accounting, (i) acquisition-related costs, except for those costs incurred to issue debt or equity securities, will be expensed in the period incurred; (ii) non-controlling interests will be valued at fair value at the acquisition date; (iii) in-process research and development will be recorded at fair value as an intangible asset at the acquisition date and amortized once the technology reaches technological feasibility; (iv) restructuring costs associated with a business combination will be expensed subsequent to the acquisition date; and (v) changes in deferred tax asset valuation allowances and income tax uncertainties after the acquisition date will be recognized through income tax expense or directly in contributed capital. The aggregate amount of consideration paid by the Company is allocated to net tangible assets and intangible assets based on their estimated fair values as of the acquisition date. The excess of the purchase price over the value of the net tangible assets and intangible assets is recorded to goodwill. The measurement of fair value of assets acquired and liabilities assumed requires significant judgment. The valuation of intangible assets, in particular, requires that the Company use valuation techniques such as the income approach. The income approach includes the use of a discounted cash flow model, which includes discounted cash flow scenarios and requires the following significant estimates: revenue, expenses, capital spending and other costs, and discount rates based on the respective risks of the cash flows.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets The Company's intangible assets include goodwill and other intangible assets. Goodwill is recorded when the purchase price paid for an acquisition exceeds the estimated fair value of the net identified tangible and intangible assets acquired. Other intangible assets include existing technologies, core and developed technology, in-process research and development, trademarks and trade names, distribution rights and customer-related intangibles. In-process research and development 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. Indefinite-lived intangible assets consist of goodwill and in-process research and development intangible assets that have not yet been placed in service. All other intangible assets are definite-lived intangible assets, including in-process research and development assets that have been placed in service, and are amortized over their respective estimated lives, ranging from 1 to 15 years. The Company is required to perform an impairment review of indefinite-lived intangible assets, including goodwill annually, and more frequently under certain circumstances. Indefinite-lived intangible assets are subjected to this annual impairment test during the fourth quarter of the Company's fiscal year. The Company engages primarily in the development, manufacture and sale of semiconductor products as well as technology licensing. As a result, the Company concluded there are two reporting units, semiconductor products and technology licensing. Under the qualitative indefinite-lived intangible asset impairment assessment standard, management evaluates whether it is more likely than not that the indefinite-lived intangible assets are impaired. If it is determined that it is more likely than not, the Company proceeds with the next step of the impairment test, which compares the fair value of the reporting unit or indefinite-lived intangible asset to its carrying value. If the Company determines through the impairment process that the indefinite-lived intangible asset has been impaired, the Company will record the impairment charge in its results of operation. Through March 31, 2018, the Company has not had impaired goodwill. In the event that facts and circumstances indicate definite-lived intangible assets may be impaired, the Company evaluates the recoverability and estimated useful lives of such assets. If such indicators are present, recoverability is evaluated based on whether the sum of the estimated undiscounted cash flows attributable to the asset (group) in question is less than their carrying value. If less, the Company measures the fair value of the asset (group) and recognizes an impairment loss if the carrying amount of the assets exceeds their respective fair values.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company assesses whether indicators of impairment of long-lived assets are present. If such indicators are present, the Company determines whether the sum of the estimated undiscounted cash flows attributable to the assets in question is less than their carrying value. If less, the Company recognizes an impairment loss based on the excess of the carrying amount of the assets over their respective fair values. Fair value is determined by discounted future cash flows, appraisals or other methods. If the assets determined to be impaired are to be held and used, the Company recognizes an impairment loss through a charge to operating results to the extent the present value of anticipated net cash flows attributable to the asset are less than the asset's carrying value. The Company would depreciate the remaining value over the remaining estimated useful life of the asset.
Share-Based Compensation	Share-Based Compensation The Company has equity incentive plans under which non-qualified stock options and restricted stock units (RSUs) have been granted to employees and non-employee members of the Board of Directors. For the past several years the Company has adopted RSUs as its primary equity incentive compensation instrument for employees. The Company also has employee stock purchase plans for eligible employees. Share-based compensation cost is measured on the grant date based on the fair market value of the Company’s common stock discounted for expected future dividends and is recognized as expense on a straight-line basis over the requisite service periods. If there are any modifications or cancellations of the underlying unvested securities, the Company may be required to accelerate or increase any remaining unearned share-based compensation expense. Future share-based compensation expense and unearned share-based compensation will increase to the extent that the Company grants additional equity awards to employees or it assumes unvested equity awards in connection with acquisitions. During fiscal 2017, the Company elected to early adopt ASU 2016-09-Compensation - Stock Compensation, Improvements to Employee Share-Based Payment Accounting (Topic 718). See "Recently Adopted Accounting Pronouncements" for additional information on the new guidance.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of investments in debt securities and trade receivables. Investments in debt securities with original maturities of greater than six months consist primarily of AAA and AA rated financial instruments and counterparties. The Company's investments are primarily in direct obligations of the U.S. government or its agencies, corporate bonds, and municipal bonds. Concentrations of credit risk with respect to accounts receivable are generally not significant due to the diversity of the Company's customers and geographic sales areas. The Company sells its products primarily to OEMs and distributors in the Americas, Europe and Asia. The Company performs ongoing credit evaluations of its customers' financial condition and, as deemed necessary, may require collateral, primarily letters of credit. Distributor advances, included in deferred income on shipments to distributors in the consolidated balance sheets, totaled $203.9 million at March 31, 2018 and March 31, 2017. On sales to distributors, the Company's payment terms generally require the distributor to settle amounts owed to the Company for an amount in excess of their ultimate cost. The Company's sales price to its distributors may be higher than the amount that the distributors will ultimately owe the Company because distributors often negotiate price reductions after purchasing the products from the Company and such reductions are often significant. It is the Company's practice to apply these negotiated price discounts to future purchases, requiring the distributor to settle receivable balances, on a current basis, generally within 30 days, for amounts originally invoiced. This practice has an adverse impact on the working capital of the Company's distributors. As such, the Company has entered into agreements with certain distributors whereby it advances cash to the distributors to reduce the distributors' working capital requirements. These advances are reconciled at least on a quarterly basis and are estimated based on the amount of ending inventory as reported by the distributor multiplied by a negotiated percentage. Such advances have no impact on revenue recognition or the Company's consolidated statements of income. The Company processes discounts taken by distributors against its deferred income on shipments to distributors' balance and trues-up the advanced amounts generally after the end of each completed fiscal quarter. The terms of these advances are set forth in binding legal agreements and are unsecured, bear no interest on unsettled balances and are due upon demand. The agreements governing these advances can be canceled by the Company at any time.
Use of Estimates	Use of Estimates The Company has made a number of estimates and assumptions relating to the reporting of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities to prepare its consolidated financial statements in conformity with U.S. Generally Accepted Accounting Principles. Actual results could differ from those estimates.
Business Segments	Business Segments Operating segments are components of an enterprise about which separate financial information is regularly reviewed by the chief operating decision makers ("CODMs") to assess the performance of the component and make decisions about the resources to be allocated to the component. The Company's Chairman and Chief Executive Officer and the Company's President and Chief Operating Officer have been identified as the CODMs as they jointly manage the Company's worldwide consolidated enterprise. Based on the Company's structure and manner in which the Company is managed and decisions are made, the Company's business is made up of two operating segments, semiconductor products and technology licensing. In the semiconductor products segment, the Company designs, develops, manufactures and markets microcontrollers, development tools and analog, interface, mixed-signal, timing, wired and wireless connectivity devices, and memory products. Under the leadership of the CODMs, the Company is structured and organized around standardized roles and responsibilities based on product groups and functional activities. The Company's product groups are responsible for product research, design and development. The Company's functional activities include sales, marketing, manufacturing, information technology, human resources, legal and finance. The Company's product groups have similar products, production processes, types of customers and methods for distribution. In addition, the tools and technologies used in the design and manufacture of the Company's products are shared among the various product groups. The Company's product group leaders, under the direction of the CODMs, define the product roadmaps and team with sales personnel to achieve design wins and revenue and other performance targets. Product group leaders also interact with manufacturing and operational personnel who are responsible for the production, prioritization and planning of the Company's manufacturing capabilities to help ensure the efficiency of the Company's operations and fulfillment of customer requirements. This centralized structure supports a global operating strategy in which the CODMs assess performance and allocate resources based on the Company's consolidated results.
Recently Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements During the three months ended June 30, 2017, the Company adopted ASU 2015-11-Simplifying the Measurement of Inventory. This standard requires that entities measure inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. ASU 2015-11 is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2016 and is applied prospectively. The adoption of this standard did not have a material impact on the Company's financial statements. During the three months ended June 30, 2017, the Company elected to early adopt ASU 2017-07-Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. This standard improves the presentation of net periodic pension cost and net periodic postretirement benefit cost. The amendment will require the employer to report the service cost component in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost will be presented separately in the income statement from the service cost component outside of income from operations. The amendment is effective for fiscal years beginning after December 15, 2017. Early adoption is permitted at the beginning of an annual period (in the first interim period) for which financial statements have not yet been issued. The adoption of this standard did not have a material impact on the Company's financial statements. During the three months ended June 30, 2016, the Company elected to early adopt ASU 2016-09-Compensation - Stock Compensation, Improvements to Employee Share-Based Payment Accounting (Topic 718), which simplifies several aspects of the accounting for share-based payment transactions. Under this standard, entities are permitted to make an accounting policy election to either estimate forfeitures on share-based payment awards, as previously required, or to recognize forfeitures as they occur. The Company elected to recognize forfeitures as they occur and the impact of that change in accounting policy was recorded as a $2.0 million cumulative effect adjustment as an increase to the Company's retained earnings and a decrease to additional paid-in capital as of April 1, 2016. The Company also recorded a cumulative-effect adjustment to retained earnings for the increase of $2.3 million in long-term deferred tax assets related to the forfeiture rate reduction on outstanding share-based payment awards. Additionally, ASU 2016-09 eliminates the requirement to report excess tax benefits and certain tax deficiencies related to share-based payment transactions in additional paid-in capital. In accordance with the new standard, the Company will record excess tax benefits and tax deficiencies as income tax benefit or provision on a prospective basis in its consolidated statements of income. The standard also eliminates the requirement that excess tax benefits be realized before companies can recognize them. Accordingly, the Company has recorded a $47.2 million cumulative-effect adjustment to its retained earnings and long-term deferred tax assets as of April 1, 2016 for previously unrecognized excess tax benefits. ASU 2016-09 also requires excess tax benefits to be reported as operating activities in the statement of cash flows rather than as a financing activity. The Company has elected to apply the change in cash flow classification on a prospective basis and prior periods were not retrospectively adjusted. Recently Issued Accounting Pronouncements Not Yet Adopted In August 2017, the FASB issued ASU 2017-12-Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. The update expands an entity's ability to apply hedge accounting for nonfinancial and financial risk components and allows for a simplified approach for fair value hedging of interest rate risk. The update eliminates the need to separately measure and report hedge ineffectiveness and generally requires the entire change in fair value of a hedging instrument to be presented in the same income statement line as the hedged item. Additionally, the update simplifies the hedge documentation and effectiveness assessment requirements under the previous guidance. The effective date of this standard is for fiscal years beginning after December 15, 2018 and early adoption is permitted. Adoption will be applied through a cumulative-effect adjustment for cash flow and net investment hedges existing at the date of adoption and prospectively for presentation and disclosure. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statements. In January 2017, the FASB issued ASU 2017-04-Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment, which simplifies the accounting for goodwill impairment. The guidance removes Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. A goodwill impairment will now be the amount by which a reporting unit's carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. The amendment is effective for annual periods and interim periods within those annual periods, beginning after December 15, 2019, and early adoption is permitted. The Company does not expect this standard to have an impact on its consolidated financial statements. In June 2016, the FASB issued ASU 2016-13-Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments. This standard requires entities to use a current lifetime expected credit loss methodology to measure impairments of certain financial assets. Using this methodology will result in earlier recognition of losses than under the current incurred loss approach, which required waiting to recognize a loss until it is probable of having been incurred. The amendments in ASU 2016-13 broaden the information that an entity must consider in developing its expected credit loss estimate for assets measured either collectively or individually and can include forecasted information. There are other provisions within the standard affecting how impairments of other financial assets may be recorded and presented, as well as expanded disclosures. ASU 2016-13 is effective for interim and annual periods beginning after December 15, 2019, and permits early adoption, but not before December 15, 2018. The standard is to be applied using a modified retrospective approach. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statements. In October 2016, the FASB issued ASU 2016-16-Intra-Entity Transfers of Assets Other Than Inventory. This standard addresses the recognition of current and deferred income taxes resulting from an intra-entity transfer of any asset other than inventory. Prior to the adoption of ASU 2016-16, a company will defer for financial reporting purposes the income tax expense resulting from an intra-entity asset transfer, including the taxes currently payable or paid. Upon adoption of ASU 2016-16, a company will recognize current and deferred income taxes that result from such transfers in the period in which they occur. ASU 2016-16 is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017 and is applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. The Company is currently evaluating the impact of the adoption of this standard will have on its consolidated financial statements but expects to recognize its previously deferred tax related to intra-entity transfers upon adoption of ASU 2016-16 as of April 1, 2018 with an estimated impact of up to $1.6 billion cumulative-effect increase to retained earnings. In November 2016, the FASB issued ASU 2016-18-Statement of Cash Flows: Restricted Cash. This standard requires that the statement of cash flows explain the change during the period in total cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. The standard is to be applied using a retrospective transition method to each period presented. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02-Leases. This standard requires lessees to recognize a lease liability and a right-of-use asset on the balance sheet and aligns many of the underlying principles of the new lessor model with those in Accounting Standards Codification Topic 606, Revenue from Contracts with Customers. ASU 2016-02 is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2018, with early adoption permitted. The standard is to be applied using the modified retrospective approach to all periods presented. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statements. In January 2016, the FASB issued ASU 2016-01-Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. This standard addresses certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. ASU 2016-01 is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017. Early adoption is not permitted. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statements. In May 2014, the FASB issued ASU 2014-09-Revenue from Contracts with Customers (Topic 606), which superseded nearly all existing revenue recognition guidance under US GAAP. In August 2015, the FASB issued ASU 2015-14-Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which delayed the effective date of the new standard by one year to December 15, 2017, for annual and interim reporting periods beginning after that date. In accordance with the delay, the new standard was effective for the Company beginning April 1, 2018. 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 new standard allows for the amendment to be applied either retrospectively to each prior reporting period presented or retrospectively as a cumulative-effect adjustment as of the date of adoption. In March 2016, the FASB issued ASU 2016-08-Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net), which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10-Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies the implementation guidance on identifying performance obligations. In May 2016, the FASB issued ASU 2016-12-Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, which addresses implementation issues that were raised by stakeholders and discussed by the Revenue Recognition Transition Resource Group. The Company will adopt the standard under the modified retrospective transition method on April 1, 2018. As described in the Company's significant accounting policies, the Company currently defers the revenue and cost of sales on shipments to distributors until the distributor sells the product to their end customer. Upon adoption of ASU 2014-09, ASU 2015-14, ASU 2016-08, ASU 2016-10 and ASU 2016-12, the Company will no longer defer revenue until sale by the distributor to the end customer, but rather, will be required to estimate the effects of returns and allowances provided to distributors and record revenue at the time of sale to the distributor. The impact of the adoption of the standard on the Company's April 1, 2018 consolidated balance sheet is expected to include: the elimination of the entire deferred income balance as of April 1, 2018 of $334 million; a net decrease in accounts receivable of between $41 million and $51 million; an increase in accrued liabilities of between $10 million and $14 million; an increase in other current assets of between $14 million and $18 million; a decrease in inventories of between $4 million and $6 million; and an increase in retained earnings of between $219.0 million and $259.0 million, which includes the tax impact of adoption of between $38.0 million and $58.0 million. The tax impact of adoption offsets the increase to retained earnings, and also affects the Company's deferred tax balances. The change in timing of revenue recognized for sales to distributors is the primary contributor to the expected impact on the Company's April 1, 2018 consolidated balance sheet. To a lesser extent, changes in timing of revenue recognition in the Company's licensing contracts and changes from point-in-time to over-time revenue recognition for a few of the Company's contracts also contribute to the expected impact.