Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Net Income (Loss) Attributable to Parent [Abstract]
Net earnings (loss) attributable to Kirby	$ 17,434	$ (3,375)
Undistributed earnings allocated to restricted shares	(3)	0
Earnings (loss) available to common stockholders, basic, total	17,431	(3,375)
Undistributed earnings allocated to restricted shares	3	0
Undistributed earnings reallocated to restricted shares	(3)	0
Earnings (loss) available to Kirby common stockholders - diluted	$ 17,431	$ (3,375)
Shares outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	60,182	60,074
Weighted average unvested restricted stock (in shares)	(9)	(58)
Weighted Average Number of Shares Outstanding, Basic (in Shares)	60,173	60,016
Dilutive effect of stock options and restricted stock units (in shares)	290	0
Weighted Average Number of Shares Outstanding, Diluted (in Shares)	60,463	60,016
Net earnings (loss) per share attributable to Kirby common stockholders
Basic (in dollars per share)	$ 0.29	$ (0.06)
Diluted (in dollars per share)	$ 0.29	$ (0.06)
Antidilutive securities excluded from computation of earnings per share (in shares)	400,000	600,000
RSUs [Member]
Net earnings (loss) per share attributable to Kirby common stockholders
Antidilutive securities excluded from computation of earnings per share (in shares)	0	7,000