Note 7 - Fair Value of Assets and Liabilities - Level 3 Measurements (Details) - Industrial [Member] - Custom Products Reporting Unit [Member] - Fair Value, Inputs, Level 3 [Member] $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($)
Trade Names [Member]
Fair value	$ 680
Trade Names [Member] \| Relief From Royalty [Member]
Discount rate	18.00%
Royalty rate	1.00%
Customer Relationships [Member]
Fair value
Customer Relationships [Member] \| Excess Earnings [Member]
Discount rate	18.00%
Attrition rate	5.00%

Percentage of adjustment due to the attrition rate of an asset or liability, used as an input to measure fair value.

No definition available.

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- Definition

Percentage of adjustment for the royalty rate on an asset or liability, used as an input to measure fair value.

+ References

No definition available.

+ Details

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Namespace Prefix:	lfus_
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Period Type:	duration

- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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- Definition

Fair value portion of assets, excluding financial assets, that lack physical substance, having a limited useful life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19190-110258

+ Details

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- Details

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- Details

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- Details

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- Details

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