Note 2 - Acquisition of Businesses (Details) - Final Purchase Price Allocations (USD $) In Thousands, unless otherwise specified	Jun. 28, 2014	Dec. 28, 2013
Note 2 - Acquisition of Businesses (Details) - Final Purchase Price Allocations [Line Items]
Goodwill	$ 201,769	$ 186,464
Trademarks [Member] \| SymCom, Inc. [Member]
Note 2 - Acquisition of Businesses (Details) - Final Purchase Price Allocations [Line Items]
Amortizable intangible assets	17,020
Trademarks [Member] \| Hamlin, Inc. [Member]
Note 2 - Acquisition of Businesses (Details) - Final Purchase Price Allocations [Line Items]
Amortizable intangible assets	6,522
Patents [Member] \| SymCom, Inc. [Member]
Note 2 - Acquisition of Businesses (Details) - Final Purchase Price Allocations [Line Items]
Amortizable intangible assets	1,500
Distribution Rights [Member] \| Hamlin, Inc. [Member]
Note 2 - Acquisition of Businesses (Details) - Final Purchase Price Allocations [Line Items]
Amortizable intangible assets	35,327
Patents and Licenses [Member] \| Hamlin, Inc. [Member]
Note 2 - Acquisition of Businesses (Details) - Final Purchase Price Allocations [Line Items]
Amortizable intangible assets	16,276
SymCom, Inc. [Member]
Note 2 - Acquisition of Businesses (Details) - Final Purchase Price Allocations [Line Items]
Cash	325
Current assets, net	9,479
Property, plant and equipment	11,193
Goodwill	14,738
Other non-current assets	20
Current liabilities	(1,182)
Total purchase price allocation	53,093
Hamlin, Inc. [Member]
Note 2 - Acquisition of Businesses (Details) - Final Purchase Price Allocations [Line Items]
Cash	15,984
Current assets, net	27,811
Property, plant and equipment	24,728
Goodwill	51,218
Non-current assets	2,452
Current liabilities	(7,734)
Non-current liabilities	(12,217)
Total purchase price allocation	$ 160,367

Name:	lfus_Note2AcquisitionofBusinessesDetailsFinalPurchasePriceAllocationsLineItems
Namespace Prefix:	lfus_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

+ Details

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

- Definition

Amount of assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer, acquired at the acquisition date.

+ References

+ Details

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

- Definition

Amount of liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date.

+ References

+ Details

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

- Definition

Amount of intangible assets, excluding goodwill, acquired at the acquisition date.

+ References

+ Details

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

- Definition

Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 55

-Paragraph 37

-URI http://asc.fasb.org/extlink&oid=35744172&loc=d3e2207-128464

+ Details

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

- Definition

Amount of assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.

+ References

+ Details

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

- Definition

Amount of liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

+ References

+ Details

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

- Definition

Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.

+ References

+ Details

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

- Definition

The amount of property, plant, and equipment recognized as of the acquisition date.

+ References

+ Details

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

- 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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

+ Details

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