Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 06, 2021
Cover [Abstract]
Entity Registrant Name	KIRBY CORP
Entity Central Index Key	0000056047
Current Fiscal Year End Date	--12-31
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Document Transition Report	false
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, 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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		60,105,000