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Lease Commitments - Narrative (Details) $ in Thousands | 12 Months Ended
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Jan. 01, 2022 USD ($) renewal | Dec. 26, 2020 USD ($) | Dec. 28, 2019 USD ($)
Leases [Abstract] |  |  |
Number of renewal options | renewal | 1 |  |
Operating lease, rent expense | $ | $ 11,439 | $ 10,410 | $ 10,100

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- Definition Lessor, Operating Lease, Number Of Renewal Options + References No definition available. + Details
Name: | lfus_LessorOperatingLeaseNumberOfRenewalOptions
Namespace Prefix: | lfus_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_LeasesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of operating lease expense. Excludes sublease income. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918638-209977 + Details
Name: | us-gaap_OperatingLeaseExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration