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Earnings Per Share - Narrative (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jan. 17, 2018 | Dec. 26, 2020 | Dec. 28, 2019 | Dec. 29, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share |  |  |  |
Antidilutive securities excluded (in shares) |  | 222,526 | 129,658 | 42,305
Purchase of common stock (in shares) |  | 175,110 | 579,916 | 391,972
Repurchases of common stock |  | $ 22,927 | $ 95,036 | $ 67,908
IXYS Corporation |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share |  |  |  |
Stock issues for acquisitions (in shares) | 2,100,000 |  |  |
IXYS Corporation | Conversion of IXYS Equity Awards Into Littlefuse Equity Awards |  |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share |  |  |  |
Conversion of stock (in shares) | 500,000 |  |  |

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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- Definition The number of new shares issued in the conversion of stock in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4332-108586 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4313-108586 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586 + Details
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