Document And Entity Information - shares	3 Months Ended
	Mar. 30, 2019	Apr. 29, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	LITTELFUSE INC /DE
Entity Central Index Key	0000889331
Current Fiscal Year End Date	--12-29
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		24,726,692
Document Type	10-Q
Document Period End Date	Mar. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false