v3.8.0.1
Document And Entity Information - shares
3 Months Ended
Mar. 31, 2018
Apr. 27, 2018
Document Information [Line Items]    
Entity Registrant Name LITTELFUSE INC /DE  
Entity Central Index Key 0000889331  
Trading Symbol lfus  
Current Fiscal Year End Date --12-29  
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)   24,966,975
Document Type 10-Q  
Document Period End Date Mar. 31, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q1  
Amendment Flag false