Segment Information - Depreciation And Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 28, 2024	Dec. 30, 2023	Dec. 31, 2022
Segment Reporting Information
Depreciation	$ 68,325	$ 71,634	$ 65,011
Amortization	62,127	65,794	55,695
Electronics
Segment Reporting Information
Depreciation	40,456	39,461	35,496
Amortization	39,362	39,883	32,698
Transportation Segment
Segment Reporting Information
Depreciation	22,117	26,732	25,647
Amortization	13,518	15,782	18,109
Industrial
Segment Reporting Information
Depreciation	5,752	5,441	3,868
Amortization	$ 9,247	$ 10,129	$ 4,888

The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

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

- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-1

+ Details

Name:	us-gaap_Depreciation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=lfus_ElectronicsSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=lfus_TransportationSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=lfus_IndustrialSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: