Document And Entity Information (USD $)	12 Months Ended
	Dec. 29, 2012	Feb. 15, 2013	Jun. 30, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	LITTELFUSE INC /DE
Document Type	10-K
Current Fiscal Year End Date	--12-29
Entity Common Stock, Shares Outstanding		23,608,450
Entity Public Float			$ 1,233,164,821
Amendment Flag	false
Entity Central Index Key	0000889331
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Document Period End Date	Dec. 29, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	FY