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Nature of the Business and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands |  |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | ---
Nov. 02, 2020 USD ($) $ / shares shares | Oct. 14, 2020 USD ($) | Mar. 28, 2020 USD ($) | Mar. 27, 2020 USD ($) Location | Mar. 31, 2020 USD ($) | Oct. 31, 2017 | Dec. 25, 2020 USD ($) Location | Mar. 27, 2020 USD ($) Location | Dec. 25, 2020 USD ($) Location | Mar. 27, 2020 USD ($) Location
Percentage of ownership interest sold |  |  |  |  |  | 0.288 |  |  |  |
Number of locations | Location |  |  |  |  |  |  |  |  | 16 | 16
Number of continents on which entity operates | Location |  |  |  | 4 |  |  | 4 | 4 | 4 | 4
Proceeds from lines of credit |  |  |  |  |  |  |  |  |  | $ 43,000
Equity investment in related party |  |  |  |  |  |  | $ 26,657 |  | $ 26,657 |
Income from equity method investments |  |  |  |  |  |  | 949 |  | 1,407 |
Cash tax benefits of net operating loses |  |  |  | $ 8,963 |  |  |  |  |  |
Quality improvement property changes |  |  |  | 1,680 |  |  |  |  |  |
Defer Payment of payroll taxes |  |  |  | 2,766 |  |  |  |  |  |
Payroll taxes paid back |  |  |  | $ 1,383 |  |  |  |  |  |
COVID-19 |  |  |  |  |  |  |  |  |  |
Proceeds from lines of credit |  |  |  |  | $ 43,000 |  |  | $ 43,000 |  |
Sanken |  |  |  |  |  |  |  |  |  |
Related party debt |  |  | $ 42,700 |  |  |  |  |  |  |
Ownership percentage by majority shareholder |  |  | 70.00% |  |  |  |  |  |  |
Disposal Group, Disposed of by Sale, Not Discontinued Operations |  |  |  |  |  |  |  |  |  |
Adjustments to additional paid in capital, capitalization changes |  |  |  |  |  |  |  |  |  | $ 42,700
Related party debt |  |  | $ 66,377 |  |  |  |  |  |  |
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Sanken |  |  |  |  |  |  |  |  |  |
Ownership percentage by majority shareholder |  |  |  | 70.00% |  |  |  | 70.00% |  | 70.00%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | PSL |  |  |  |  |  |  |  |  |  |
Adjustments to additional paid in capital, capitalization changes |  |  | 42,700 |  |  |  |  |  | 19,165 |
Adjustments to additional paid in capital, income tax benefit from noncash or part non cash divestiture |  |  | 15,000 |  |  |  | 1,552 |  | 1,552 |
Related party debt |  |  | $ 66,377 |  |  |  |  |  |  |
Recievable balance net |  | $ 51,377 |  |  |  |  |  |  |  |
Accrued interest repaid |  | $ 762 |  |  |  |  |  |  |  |
Equity method investment, ownership percentage |  |  | 30.00% |  |  |  |  |  |  |
Equity investment in related party |  |  | $ 25,250 |  |  |  |  |  |  |
Income from equity method investments |  |  |  |  |  |  | $ 949 |  | $ 1,407 |
Disposal Group, Disposed of by Sale, Not Discontinued Operations | PSL | Sanken |  |  |  |  |  |  |  |  |  |
Ownership percentage by majority shareholder |  |  | 70.00% |  |  |  |  |  |  |
IPO |  |  |  |  |  |  |  |  |  |
Number of shares issued in transaction | shares | 28,750,000 |  |  |  |  |  |  |  |  |
Offering price | $ / shares | $ 14.00 |  |  |  |  |  |  |  |  |
Net proceeds | $ 321,425 |  |  |  |  |  |  |  |  |
Underwriting discounts | 20,125 |  |  |  |  |  |  |  |  |
Estimated offering costs | $ 8,450 |  |  |  |  |  |  |  |  |
IPO | Allegro Micro Systems Inc |  |  |  |  |  |  |  |  |  |
Number of shares issued in transaction | shares | 25,000,000 |  |  |  |  |  |  |  |  |
IPO - Selling Shareholders |  |  |  |  |  |  |  |  |  |
Number of shares issued in transaction | shares | 3,750,000 |  |  |  |  |  |  |  |  |
Subsequent Event | IPO |  |  |  |  |  |  |  |  |  |
Number of shares issued in transaction | shares | 28,750,000 |  |  |  |  |  |  |  |  |
Offering price | $ / shares | $ 14.00 |  |  |  |  |  |  |  |  |
Net proceeds | $ 321,425 |  |  |  |  |  |  |  |  |
Underwriting discounts | 20,125 |  |  |  |  |  |  |  |  |
Estimated offering costs | $ 8,450 |  |  |  |  |  |  |  |  |
Subsequent Event | IPO | Allegro Micro Systems Inc |  |  |  |  |  |  |  |  |  |
Number of shares issued in transaction | shares | 25,000,000 |  |  |  |  |  |  |  |  |
Subsequent Event | IPO - Selling Shareholders |  |  |  |  |  |  |  |  |  |
Number of shares issued in transaction | shares | 3,750,000 |  |  |  |  |  |  |  |  |

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