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Benefit Plans - Defined Contribution and Other Plans (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 28, 2019 | Dec. 29, 2018 | Dec. 30, 2017
401(K) Savings Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer matching contribution | 100.00% |  |
Discretionary matching contribution | 4.00% |  |
Discretionary matching contribution | 2.00% |  |
Discretionary contribution amount | $ 5.6 | $ 4.5 | $ 3.5
Supplemental Employee Retirement Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Discretionary contribution amount | 0.4 |  |
Other Long-term Liabilities |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Recorded liability | 10.5 |  |
Other Assets |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Plan assets | $ 10.5 |  |

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- Definition Percentage of employees' gross pay for which the employer contributes an additional discretionary matching contribution to a defined contribution plan. + References No definition available. + Details
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Namespace Prefix: | lfus_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of asset, recognized in statement of financial position, for assets in a defined contribution plan. + References No definition available. + Details
Name: | lfus_DefinedContributionPlanPlanAssets
Namespace Prefix: | lfus_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The carrying amount of the liability as of the balance sheet date to an individual under a deferred compensation arrangement. This amount may be the result of periodic accruals made over the period of active employment, or reflect termination benefits resulting contractual terms or a death benefit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 710 -SubTopic 10 -Section 30 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363 + Details
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Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage employer matches of the employee's percentage contribution matched. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
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- Details
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- Details
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- Details
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