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Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2020
Jan. 31, 2021
Jun. 30, 2020
Cover [Abstract]      
Document Type 10-K    
Document Fiscal Period Focus FY    
Document Annual Report true    
Document Period End Date Dec. 31, 2020    
Document Transition Report false    
Amendment Flag false    
Document Fiscal Year Focus 2020    
Current Fiscal Year End Date --12-31    
Entity File Number 1-32190    
Entity Registrant Name NEWMARKET CORPORATION    
Entity Central Index Key 0001282637    
Entity Incorporation, State or Country Code VA    
Entity Tax Identification Number 20-0812170    
Entity Address, Address Line One 330 South Fourth Street    
Entity Address, City or Town Richmond    
Entity Address, State or Province VA    
Entity Address, Postal Zip Code 23219-4350    
City Area Code 804    
Local Phone Number 788-5000    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Title of 12(b) Security Common Stock, with no par value    
Trading Symbol NEU    
Security Exchange Name NYSE    
Entity Public Float     $ 3,166,356,273
Entity Common Stock, Shares Outstanding   10,921,342  
Documents Incorporated by Reference [Text Block]
DOCUMENTS INCORPORATED BY REFERENCE
Portions of NewMarket Corporation’s definitive Proxy Statement for its 2021 Annual Meeting of Shareholders to be filed with the Securities and Exchange Commission pursuant to Regulation 14A under the Securities Exchange Act of 1934 are incorporated by reference into Part III of this Annual Report on Form 10-K.