Nature of the Business and Basis of Presentation	12 Months Ended
Nature of the Business and Basis of Presentation	Mar. 25, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	Nature of the Business and Basis of Presentation Allegro MicroSystems, Inc., together with its consolidated subsidiaries (“AMI” or the “Company”), is a global leader in designing, developing and manufacturing sensing and power solutions for motion control and energy-efficient systems in automotive and industrial markets. The Company was incorporated under the laws of Delaware on March 30, 2013 under the name of Sanken North America, Inc. (“SKNA”) as a wholly owned subsidiary of Sanken Electric Co., Ltd. (“Sanken”). In October 2017, Sanken sold 28.8% of the common stock of SKNA to One Equity Partners (“OEP”). In April 2018, SKNA filed a certificate of amendment in the state of Delaware to change its name to Allegro MicroSystems, Inc. The Company is headquartered in Manchester, New Hampshire and has a global footprint with 16 locations across four continents. On November 2, 2020, the Company completed its Initial Public Offering (“IPO”) of 28,750,000 shares of its common stock at an offering price of $14.00 per share, of which 25,000,000 shares were sold by the Company and 3,750,000 shares were sold by selling stockholders, resulting in net proceeds to the Company of approximately $321,425 after deducting $20,125 of underwriting discounts and $8,450 of offering costs. The Company’s common stock is now listed on the Nasdaq Global Select Market under the ticker symbol “ALGM.” On March 28, 2020, the Company entered into an agreement to divest a majority of its ownership interest in Polar Semiconductor, Inc. (“PSL”) to Sanken, in order to better align with its fabless, asset-lite scalable manufacturing strategy (the “PSL Divestiture”). In order to affect this in-kind, non-cash transaction, Sanken contributed the forgiveness of the fair value of the entire related party notes payable of $42,700 owed to Sanken and the Company contributed the forgiveness of the fair value of $15,000 out of the $66,377 total debt owed by PSL to the Company, which was previously eliminated in consolidation. The entire net receivable balance of $51,377 plus accrued interest of $762 was repaid on October 14, 2020. Following the divestiture, Sanken held a 70% majority share in PSL with the Company retaining a 30% minority shareholder interest. The investment was recorded for the 30%, totaling $25,250 at the divestiture date. Beginning with reporting periods on and after March 28, 2020, the investment is included on the Company’s balance sheet as an equity investment in a related party, including $1,007 and $1,413 of income earned during the fiscal years ended March 25, 2022 and March 26, 2021. In addition, the difference between the fair value contributed by both parties at the consummation of this transaction and the book value was treated as an adjustment of capitalization changes related to organizational structure of affiliates and direct and indirect interests in subsidiaries within additional paid-in capital of $19,165 at March 26, 2021. This amount includes an estimated tax effect of $1,552 for the fiscal year ended March 26, 2021. On March 28, 2020, in connection with the divestiture described above, the Company also formally terminated its distribution agreement with Sanken to distribute Sanken’s products and entered into a transitional services agreement with PSL, which contracted with Sanken as its new channel for fulfillment of Sanken product sales in North America and Europe. Sanken will continue to provide distribution support for the Company’s products in Japan. See Note 21, “Related Party Transactions” for further discussion. Impact of the COVID-19 Pandemic On March 11, 2020, the COVID-19 outbreak was declared a pandemic by the World Health Organization. The pandemic has resulted in governments around the world implementing increasingly stringent measures to help control the spread of the virus, including quarantines, “shelter in place” and “stay at home” orders, travel restrictions, business curtailments, school closures and other measures. In addition, governments and central banks in several parts of the world have enacted fiscal and monetary stimulus measures to counteract the impacts of the COVID-19 pandemic. The Company continues to monitor the rapidly evolving conditions and circumstances as well as guidance from international and domestic authorities, including public health authorities, and the Company may need to take additional actions based on their recommendations. There is considerable uncertainty regarding the impact on the Company’s business stemming from current measures and potential future measures that could restrict access to the Company’s facilities, limit manufacturing and support operations and place restrictions on the Company’s workforce and suppliers. The measures implemented by various authorities related to the COVID-19 pandemic have caused the Company to change its business practices, including those related to where employees work, the distance between employees in the Company’s facilities, limitations on the in-person meetings between employees and with customers, suppliers, service providers, and stakeholders, as well as restrictions on business travel to domestic and international locations or to attend trade shows, investor conferences and other events. The full extent to which the ongoing COVID-19 pandemic adversely affects the Company’s financial performance will depend on future developments, many of which are outside of the Company’s control, are highly uncertain and cannot be predicted, including, but not limited to, the duration and spread of the pandemic, its severity, the effectiveness of actions to contain the virus or treat its impact and how quickly and to what extent normal economic and operating conditions can resume. The COVID-19 pandemic could also result in additional governmental restrictions and regulations, which could adversely affect the Company’s business and financial results. In addition, a recession, depression or other sustained adverse market impact resulting from COVID-19 could materially and adversely affect the Company’s business and its access to needed capital and liquidity. Even after the COVID-19 pandemic has lessened or subsided, the Company may continue to experience adverse impacts on its business and financial performance as a result of its global economic impact. The COVID-19 pandemic may also heighten other risks. For example, if the business impacts of COVID-19 are prolonged, this could cause the Company to recognize impairments for goodwill and certain long-lived assets including amortizable intangible assets. The Company has taken actions to mitigate its financial risk given the uncertainty in global markets caused by the COVID-19 pandemic. During the fourth quarter of fiscal year 2020, the Company borrowed $43,000 under its revolving credit facilities. The borrowing was made as part of the Company’s ongoing efforts to preserve financial flexibility in light of the current uncertainty in the global markets and related effects on the Company’s business resulting from the COVID-19 pandemic. In connection with entering into a new revolving credit facility on September 30, 2020, the Company used cash on hand to repay all amounts outstanding under the line of credit and terminated all commitments thereunder. On March 27, 2020, the Coronavirus Aid, Relief and Economic Security Act (“the CARES Act”) was signed into law. The CARES Act contains numerous tax provisions including a correction to the applicable depreciation rates available in the original Tax Cuts and Jobs Act of 2017 (“TCJA”) for Qualified Improvement Property (“QIP”), temporarily establishes a five-year carryback period for current net operating losses (“NOL”), and contains a provision for deferred payment of 2020 employer payroll taxes. The Company currently estimates cash tax benefits of the QIP adjustment and NOL carryback period to be $12.8 million. Financial Periods The Company’s fiscal year is the 52-week or 53-week period ending on the Friday closest to the last day in March. The Company’s 2022 fiscal year ended March 25, 2022 (“fiscal year 2022”), 2021 fiscal year ended March 26, 2021 (“fiscal year 2021”) and 2020 fiscal year ended March 27, 2020 (“fiscal year 2020”) were 52-week periods.