Note 14 - Comprehensive Income and Accumulated Other Comprehensive Income (Loss) (AOCI) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 30, 2013	Dec. 29, 2012
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Accumulated Tax	$ 11,929	$ 11,819
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Accumulated Tax	$ 0	$ 0

Other comprehensive income (loss), unrealized holding gain (loss) on securities arising during period, accumulated tax.

No definition available.

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