Annualized Sales

No definition available.

Name:	lfus_AnnualizedSales
Namespace Prefix:	lfus_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Amortization Inventory

+ References

No definition available.

+ Details

Name:	lfus_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAmortizationInventory
Namespace Prefix:	lfus_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Other Non Cash Charges

+ References

No definition available.

+ Details

Name:	lfus_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherNonCashCharges
Namespace Prefix:	lfus_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Restricted Cash And Cash Equivalents

+ References

No definition available.

+ Details

Name:	lfus_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRestrictedCashAndCashEquivalents
Namespace Prefix:	lfus_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Inventory Amortization Period

+ References

No definition available.

+ Details

Name:	lfus_InventoryAmortizationPeriod
Namespace Prefix:	lfus_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- 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

Name:	us-gaap_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=123586518&loc=d3e1043-128460

+ Details

Name:	us-gaap_BusinessCombinationAcquisitionRelatedCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

+ Details

Name:	us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow associated with the acquisition of business during the period (for example, cash that was held by the acquired business).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3179-108585

+ Details

Name:	us-gaap_CashAcquiredFromAcquisition
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireBusinessesGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_SellingGeneralAndAdministrativeExpensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_OperatingIncomeLossMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=lfus_CarlingTechnologiesIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_CostOfSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=lfus_HartlandControlsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_CorporateNonSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=lfus_CarlingTechnologiesIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=lfus_HartlandControlsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Acquisitions - Narrative (Details) - USD ($) $ in Thousands			3 Months Ended	12 Months Ended
Acquisitions - Narrative (Details) - USD ($) $ in Thousands	Nov. 30, 2021	Jan. 28, 2021	Mar. 28, 2020	Jan. 01, 2022	Dec. 26, 2020	Dec. 28, 2019
Business Acquisition
Cash, net of cash acquired				$ 423,633	$ 0	$ 775
Acquisition related costs			$ 1,200	4,500
Restricted cash				$ 1,700
Inventory amortization period (in years)				4 months
Selling, General and Administrative Expenses
Business Acquisition
Acquisition related costs				$ 6,200	$ 800
Operating Income (Loss)
Business Acquisition
Acquisition related costs						$ 8,900
Carling Technologies
Business Acquisition
Cash	$ 315,000
Cash, net of cash acquired	313,583
Revenue of acquiree since acquisition				15,300
Loss from acquiree since acquisition				1,200
Carling Technologies \| Cost of Sales
Business Acquisition
Other noncash charges				1,600
Hartland Controls
Business Acquisition
Cash, net of cash acquired		$ 108,516
Revenue of acquiree since acquisition				100,500
Loss from acquiree since acquisition				2,800
Acquisition related costs				800
Cash acquired from acquisition		111,000
Hartland Controls \| Operating Income (Loss) \| Other
Business Acquisition
Inventory amortization adjustment				$ 6,800
Carling Technologies
Business Acquisition
Annualized sales	$ 170,000
Hartland Controls
Business Acquisition
Annualized sales		$ 70,000