Document And Entity Information - shares	9 Months Ended
	Sep. 26, 2015	Oct. 23, 2015
Entity Registrant Name	LITTELFUSE INC /DE
Entity Central Index Key	0000889331
Trading Symbol	lfus
Current Fiscal Year End Date	--12-26
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Common Stock, Shares Outstanding (in shares)		22,299,062
Document Type	10-Q
Document Period End Date	Sep. 26, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Amendment Flag	false