Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Net Income (Loss) Attributable to Parent [Abstract]
Net earnings attributable to Kirby	$ 70,068	$ 40,698
Undistributed earnings allocated to restricted shares	(1)	(2)
Earnings available to Kirby common stockholders - basic	70,067	40,696
Undistributed earnings allocated to restricted shares	1	2
Undistributed earnings reallocated to restricted shares	(1)	(2)
Earnings available to Kirby common stockholders - diluted	$ 70,067	$ 40,696
Shares outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	58,473,000	59,981,000
Weighted average unvested restricted stock (in shares)	(1,000)	(3,000)
Weighted Average Number of Shares Outstanding, Basic (in Shares)	58,472,000	59,978,000
Dilutive effect of stock options and restricted stock units (in shares)	347,000	294,000
Weighted average common stock outstanding - diluted	58,819,000	60,272,000
Net earnings per share basic attributable to Kirby common stockholders:
Basic	$ 1.2	$ 0.68
Net earnings per share diluted attributable to Kirby common stockholders:
Diluted	$ 1.19	$ 0.68
Antidilutive securities excluded from computation of earnings per share (in shares)	23,000	309,000
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