v3.8.0.1
Document And Entity Information - USD ($)
12 Months Ended
Dec. 30, 2017
Feb. 16, 2018
Jul. 01, 2017
Document Information [Line Items]      
Entity Registrant Name LITTELFUSE INC /DE    
Entity Central Index Key 0000889331    
Trading Symbol lfus    
Current Fiscal Year End Date --12-30    
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)   24,830,204  
Entity Public Float     $ 3,736,767,705
Document Type 10-K    
Document Period End Date Dec. 30, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Amendment Flag false