Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Net Income (Loss) Attributable to Parent [Abstract]
Net earnings attributable to Kirby	$ 40,698	$ 17,434
Undistributed earnings allocated to restricted shares	(2)	(3)
Earnings (loss) available to Kirby common stockholders - basic	40,696	17,431
Undistributed earnings allocated to restricted shares	2	3
Undistributed earnings reallocated to restricted shares	(2)	(3)
Earnings (loss) available to Kirby common stockholders - diluted	$ 40,696	$ 17,431
Shares outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	59,981,000	60,182,000
Weighted average unvested restricted stock (in shares)	(3,000)	(9,000)
Weighted Average Number of Shares Outstanding, Basic (in shares)	59,978,000	60,173,000
Dilutive effect of stock options and restricted stock units (in shares)	294,000	290,000
Weighted Average Number of Shares Outstanding, Diluted (in shares)	60,272,000	60,463,000
Net earnings per share basic attributable to Kirby common stockholders:
Basic	$ 0.68	$ 0.29
Net earnings per share diluted attributable to Kirby common stockholders:
Diluted	$ 0.68	$ 0.29
Antidilutive securities excluded from computation of earnings per share (in shares)	300,000	400,000
RSUs [Member]
Net earnings per share diluted attributable to Kirby common stockholders:
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0