| Document and Entity Information | Jul. 27, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | KIRBY CORPORATION |
| Entity Central Index Key | 0000056047 |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jul. 27, 2021 |
| Entity File Number | 1-7615 |
| Entity Incorporation, State or Country Code | NV |
| Entity Tax Identification Number | 74-1884980 |
| Entity Address, Address Line One | 55 Waugh Drive |
| Entity Address, Address Line Two | Suite 1000 |
| Entity Address, City or Town | Houston |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77007 |
| City Area Code | 713 |
| Local Phone Number | 435-1000 |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | KEX |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
