| Document and Entity Information | Oct. 28, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 28, 2020 |
| Entity Registrant Name | NEWMARKET CORPORATION |
| Entity Central Index Key | 0001282637 |
| Entity Incorporation, State or 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 |
| Title of 12(b) Security | Common Stock, with no par value |
| Trading Symbol | NEU |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
