Note 7 - Shareholders' Equity (Details Textual) - USD ($) $ in Millions	Jul. 01, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Pension and Other Post-retirement Benefit Plans, Liability Adjustment Tax	$ 1.1	$ 1.1

Represents accumulated Other Comprehensive Income (Loss), Pension and Other Post-retirement Benefit Plans, Liability Adjustment Tax.

No definition available.

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