Inventory step-up recorded in an acquisition.

No definition available.

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

- Definition

The amount of noncash charges relating to the inventory stepup.

+ References

No definition available.

+ Details

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

- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e1043-128460

+ Details

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

- Definition

For contingent consideration arrangements recognized in connection with a business combination, this element represents an estimate of the high-end of the potential range (undiscounted) of the consideration which may be paid.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

Name:	us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3213-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

+ Details

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

- Details

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

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_PatentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TrademarksMember
Namespace Prefix:
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Note 2 - Acquisition of Businesses (Details Textual) - USD ($) $ in Thousands			3 Months Ended							6 Months Ended	12 Months Ended
	Oct. 01, 2015	Jan. 03, 2014	Jan. 02, 2016	Sep. 26, 2015	Jun. 27, 2015	Mar. 28, 2015	Dec. 27, 2014	Jun. 28, 2014	Mar. 29, 2014	Jun. 28, 2014	Jan. 02, 2016	Jan. 02, 2016	Dec. 27, 2014	Dec. 28, 2013
Sigmar [Member] \| Patents [Member]
Finite-Lived Intangible Asset, Useful Life	10 years
Sigmar [Member]
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Payments to Acquire Businesses, Net of Cash Acquired	$ 5,400
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	$ 600
Sym Com Inc [Member] \| Patents [Member] \| Minimum [Member]
Finite-Lived Intangible Asset, Useful Life		16 years
Sym Com Inc [Member] \| Patents [Member] \| Maximum [Member]
Finite-Lived Intangible Asset, Useful Life		17 years
Sym Com Inc [Member] \| Trademarks [Member] \| Minimum [Member]
Finite-Lived Intangible Asset, Useful Life		15 years
Sym Com Inc [Member] \| Trademarks [Member] \| Maximum [Member]
Finite-Lived Intangible Asset, Useful Life		20 years
Sym Com Inc [Member]
Business Combination, Acquisition Related Costs								$ 200
Business Acquisition, Percentage of Voting Interests Acquired		100.00%
Payments to Acquire Businesses, Net of Cash Acquired		$ 52,800
Business Acquisition Inventory Stepup		$ 2,600						2,800		$ 2,800
Noncash Charges Related To Inventory Stepup								$ 1,400	$ 1,400	$ 1,400
Business Combination, Acquisition Related Costs			$ 4,000	$ 300	$ 200	$ 200	$ 300					$ 4,600	$ 500	$ 1,700
Payments to Acquire Businesses, Net of Cash Acquired											$ 4,558		$ 56,368	$ 144,382
Finite-Lived Intangible Asset, Useful Life												12 years 146 days	12 years 182 days