| Document and Entity Information | Aug. 05, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | NEWMARKET CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0001282637 |
| Document Type | 8-K |
| Document Period End Date | Aug. 5, 2021 |
| Entity Incorporation State Country Code | VA |
| Entity File Number | 1-32190 |
| 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 |
| City Area Code | (804) |
| Local Phone Number | 788-5000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, without par value |
| Trading Symbol | NEU |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
