Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Net Income (Loss) Attributable to Parent [Abstract]
Net earnings attributable to Kirby	$ 28,457	$ 10,190	$ 45,891	$ 6,815
Undistributed earnings allocated to restricted shares	(10)	(8)	(11)	(6)
Earnings available to common stockholders, basic, total	28,447	10,182	45,880	6,809
Undistributed earnings allocated to restricted shares	10	8	11	6
Undistributed earnings reallocated to restricted shares	(10)	(8)	(11)	(6)
Earnings available to Kirby common stockholders - diluted	$ 28,447	$ 10,182	$ 45,880	$ (6,809)
Shares outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	60,222	60,101	60,202	60,088
Weighted average unvested restricted stock (in shares)	(20)	(48)	(14)	(53)
Weighted Average Number of Shares Outstanding, Basic (in Shares)	60,202	60,053	60,188	60,035
Dilutive effect of stock options and restricted stock units (in shares)	265	221	277	185
Weighted Average Number of Shares Outstanding, Diluted (in Shares)	60,467	60,274	60,465	60,220
Net earnings per share basic attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 0.47	$ 0.17	$ 0.76	$ 0.11
Net earnings per share diluted attributable to Kirby common stockholders:
Diluted (in dollars per share)	$ 0.47	$ 0.17	$ 0.76	$ 0.11
Antidilutive securities excluded from computation of earnings per share (in shares)			400,000	600,000
RSUs [Member]
Net earnings per share diluted attributable to Kirby common stockholders:
Antidilutive securities excluded from computation of earnings per share (in shares)			12,000	5,000