Goodwill and Other Intangible Assets - Amounts for Goodwill and Changes in Carrying Value by Operating Segment (Details) - USD ($) $ in Thousands		12 Months Ended
Mar. 25, 2016	Dec. 29, 2018	Dec. 30, 2017
Goodwill [Roll Forward]
Balance		$ 453,414	$ 403,544
Additions		382,903	36,716
Foreign currency translation and other adjustments		(9,602)	13,154
Balance		826,715	453,414
Electronics
Goodwill [Roll Forward]
Balance		278,959	215,765
Additions	$ 103,800	382,903	36,716
Foreign currency translation and other adjustments		(5,823)	26,478
Balance		656,039	278,959
Goodwill adjustments		21,600
Automotive
Goodwill [Roll Forward]
Balance		135,829	144,585
Additions	$ 61,300	0	0
Foreign currency translation and other adjustments		(3,497)	(8,756)
Balance		132,332	135,829
Goodwill adjustments		(16,800)
Industrial
Goodwill [Roll Forward]
Balance		38,626	43,194
Additions		0	0
Foreign currency translation and other adjustments		(282)	(4,568)
Balance		38,344	$ 38,626
Goodwill adjustments		$ (4,800)

The amount of adjustments made to goodwill during the period to correct for errors.

No definition available.

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

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

+ Details

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

+ Details

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

- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

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