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Related Party Transactions (Details) - USD ($) |  |  |  |  |  |  |  |  |  | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2025 | Sep. 20, 2024 | Aug. 07, 2024 | Jul. 29, 2024 | Jul. 26, 2024 | Jul. 24, 2024 | Jul. 23, 2024 | Apr. 25, 2024 | Mar. 31, 2023 | Sep. 26, 2025 | Sep. 27, 2024 | Sep. 26, 2025 | Sep. 27, 2024 | Jun. 27, 2025 | Mar. 28, 2025
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from issuance of common stock |  |  |  |  |  |  |  |  |  |  |  |  | $ 665,850,000 |  |
Loss on change in fair value of forward repurchase contract |  |  |  |  |  |  |  |  |  | $ 0 | $ (34,752,000) | $ 0 | (34,752,000) |  |
Trade accounts receivable, net |  |  |  |  |  |  |  |  |  | 105,770,000 |  | 105,770,000 |  |  | $ 84,598,000
Selling general and administrative expenses |  |  |  |  |  |  |  |  |  | 42,158,000 | $ 38,085,000 | 89,700,000 | $ 78,282,000 |  |
Share Repurchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Facilitation fee included in transaction expenses |  |  |  |  |  |  | $ 35,000,000 |  |  |  |  |  |  |  |
Facilitation fee |  |  |  | $ 35,000,000 |  |  |  |  |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock |  |  |  |  |  |  |  |  |  |  | 28,750,000 |  | 28,750,000 |  |
Common Stock | Share Repurchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repurchase of common stock |  |  | 10,017,315 | 28,750,000 |  |  | 38,767,315 |  |  |  |  |  |  |  |
Repurchase of common stock aggregate consideration , value |  |  | $ 225,549,000 | $ 628,256,000 |  |  |  |  |  |  |  |  |  |  |
Common Stock | Equity Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from issuance of common stock |  |  |  |  | $ 665,850,000 |  |  |  |  |  |  |  |  |  |
Issuance of common stock |  |  |  |  | 28,750,000 | 25,000,000 |  |  |  |  |  |  |  |  |
Share price |  |  |  |  | $ 24 | $ 23.16 |  |  |  |  |  |  |  |  |
Underwriting discount |  |  |  |  | $ 24,150,000 |  |  |  |  |  |  |  |  |  |
Common Stock | Equity Offering | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from issuance of common stock |  |  |  |  |  |  | $ 300,000,000 |  |  |  |  |  |  |  |
Common Stock | Underwriters Option |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock |  |  |  |  |  | 3,750,000 |  |  |  |  |  |  |  |  |
Polar Semiconductor, LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extinguishment of Debt, Amount |  | $ 10,350,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Exchange for equity interests amounts of transaction |  |  |  |  |  |  |  | $ 175,000,000 |  |  |  |  |  |  |
PSL |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchases from related party |  |  |  |  |  |  |  |  |  | 9,124,000 | $ 14,378,000 | 17,394,000 | $ 29,334,000 |  |
Amounts due to related party |  |  |  |  |  |  |  |  |  | 3,263,000 |  | 3,263,000 |  |  | 6,535,000
Sanken |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other accounts receivable from related party |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 | 0
Sanken | Sanken Distribution Agreement, One-Time Sales Return |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Trade accounts receivable, net |  |  |  |  |  |  |  |  |  | $ 0 |  | $ 0 |  |  | $ 0
Selling general and administrative expenses |  |  |  |  |  |  |  |  | $ 5,000,000 |  |  |  |  |  |
Related party transaction amounts |  |  |  |  |  |  |  |  | $ 4,200,000 |  |  |  |  |  |
Distribution agreement period | 12 months |  |  |  |  |  |  |  | 24 months |  |  |  |  |  |
Sanken Electric Co., Ltd. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage by majority shareholder |  |  |  |  |  |  |  |  |  | 32.30% |  | 32.30% |  |  |
Allegro Microsystems, Inc. | Polar Semiconductor, LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage by majority shareholder |  |  |  |  |  |  |  | 10.20% |  |  |  |  |  |  |

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