Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Feb. 16, 2017	Jul. 02, 2016
Document Information [Line Items]
Entity Registrant Name	LITTELFUSE INC /DE
Entity Central Index Key	0000889331
Trading Symbol	lfus
Current Fiscal Year End Date	--12-31
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)		22,632,855
Entity Public Float			$ 2,607,309,310
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	FY
Amendment Flag	false