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Document and Entity Information - USD ($)
 12 Months Ended
Dec. 28, 2019
Mar. 12, 2020
Jun. 29, 2019
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 28, 2019    
Document Transition Report false    
Entity File Number 1-5039    
Entity Registrant Name WEIS MARKETS INC    
Entity Incorporation, State or Country Code PA    
Entity Tax Identification Number 24-0755415    
Entity Address, Address Line One 1000 S. Second Street    
Entity Address, Address Line Two P. O. Box 471    
Entity Address, City or Town Sunbury    
Entity Address, State or Province PA    
Entity Address, Postal Zip Code 17801-0471    
City Area Code 570    
Local Phone Number 286-4571    
Title of 12(b) Security Common stock, no par value    
Trading Symbol WMK    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 368,000,000
Entity Common Stock, Shares Outstanding   26,898,443  
Documents Incorporated by Reference [Text Block]

DOCUMENTS INCORPORATED BY REFERENCE:  Selected portions of the Weis Markets, Inc. definitive proxy statement dated March 12, 2020 are incorporated by reference in Part III of this Form 10-K.

   
Amendment Flag false    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2019    
Entity Central Index Key 0000105418    
Current Fiscal Year End Date --12-28