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Stock-Based Compensation - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2018 | Dec. 28, 2019 | Dec. 29, 2018 | Dec. 30, 2017 | May 01, 2019 | May 02, 2018
Authorized (in shares) |  | 1,200,000 |  |  |  |
IXYS converted awards (in shares) |  | 499,027 |  |  |  |
Allocated share based compensation |  | $ 19,900 | $ 28,200 | $ 17,300 |  |
Options intrinsic value |  | 12,500 | 38,300 | 2,200 |  |
Options vested fair value |  | 15,500 | 20,800 | 15,000 |  |
Share-based liabilities paid |  | 900 | 1,100 | 900 |  |
Unrecognized compensation cost |  | $ 17,400 |  |  |  |
Unrecognized compensation cost, period for recognition |  | 1 year 9 months 18 days |  |  |  |
Income tax benefit |  | $ 3,300 | $ 6,000 | 6,000 |  |
Share repurchase program authorized (in shares) |  |  |  |  | 1,000,000 | 1,000,000
Purchase of common stock (in shares) |  | 579,916 | 391,972 |  |  |
Repurchases of common stock |  | $ 95,036 | $ 67,908 |  |  |
Stock compensation expense |  | $ 19,046 | $ 27,431 | $ 16,315 |  |
Options |  |  |  |  |  |
Award vesting period |  | 4 years |  |  |  |
IXYS Corporation | Options |  |  |  |  |  |
Allocated share based compensation |  | $ 11,900 |  |  |  |
Minimum | Options |  |  |  |  |  |
Award vesting period |  | 3 years |  |  |  |
Award expiration period |  | 7 years |  |  |  |
Minimum | Non-vested restricted share and share unit awards |  |  |  |  |  |
Award vesting period |  | 3 years |  |  |  |
Maximum | Options |  |  |  |  |  |
Award vesting period |  | 5 years |  |  |  |
Award expiration period |  | 10 years |  |  |  |
Maximum | Non-vested restricted share and share unit awards |  |  |  |  |  |
Award vesting period |  | 4 years |  |  |  |
Selling, General and Administrative Expenses | IXYS Corporation |  |  |  |  |  |
Stock compensation expense | $ 4,500 |  |  |  |  |

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