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v3.20.1

Summary of Significant Accounting Policies and Other Information (Details Textual) customer in Thousands | 3 Months Ended
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Mar. 28, 2020 customer
Accounting Policies [Abstract] |
Number of customers (over) | 100

X
- Definition The number of customers that a company has. + References No definition available. + Details
Name: | lfus_NumberofCustomers
Namespace Prefix: | lfus_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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