Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Income (Loss) Attributable to Parent [Abstract]
Net earnings (loss) attributable to Kirby	$ 222,935	$ 122,291	$ (246,954)
Undistributed earnings allocated to restricted shares	(62)	(33)	0
Earnings (loss) available to Kirby common stockholders - basic	222,873	122,258	(246,954)
Undistributed earnings allocated to restricted shares	62	33	0
Undistributed earnings allocated to restricted shares	(62)	(33)	0
Earnings (loss) available to Kirby common stockholders - diluted	$ 222,873	$ 122,258	$ (246,954)
Shares outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	59,548,000	60,055,000	60,099,000
Weighted average unvested restricted stock (in shares)	(17,000)	(17,000)	(46,000)
Weighted Average Number of Shares Outstanding, Basic (in Shares)	59,531,000	60,038,000	60,053,000
Dilutive effect of stock options and restricted stock units (in shares)	326,000	291,000	0
Weighted Average Number of Shares Outstanding, Diluted (in Shares)	59,857,000	60,329,000	60,053,000
Net earnings (loss) per share basic attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 3.74	$ 2.04	$ (4.11)
Net earnings (loss) per share diluted attributable to Kirby common stockholders:
Diluted (in dollars per share)	$ 3.72	$ 2.03	$ (4.11)
Antidilutive securities excluded from computation of earnings per share (in shares)	33,000	381,000	567,000
Restricted Stock Units (RSUs) [Member]
Net earnings (loss) per share diluted attributable to Kirby common stockholders:
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0	7,000