Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Results (Unaudited) [Abstract]
Revenues	$ 655,927	$ 666,809	$ 771,042	$ 744,621	$ 721,493	$ 704,845	$ 802,671	$ 741,688
Costs and expenses	643,001	588,534	698,317	674,672	740,344	636,906	747,260	692,866
Gain (loss) on disposition of assets	3,251	(374)	3,118	2,157	(390)	18	442	1,898	$ 8,152	$ 1,968	$ (4,487)
Operating income	16,177	77,901	75,843	72,106	(19,241)	67,957	55,853	50,720	242,027	155,289	93,625
Other income (expense)	1,110	864	2,381	(568)	1,140	1,454	1,541	1,591
Interest expense	(12,968)	(14,310)	(15,515)	(13,201)	(12,191)	(12,345)	(12,540)	(9,780)	(55,994)	(46,856)	(21,472)
Earnings before taxes on income	4,319	64,455	62,709	58,337	(30,292)	57,066	44,854	42,531	189,820	114,159	73,014
Benefit (provision) for taxes on income	(1,347)	(16,305)	(15,269)	(13,880)	5,961	(15,116)	(16,061)	(9,865)	(46,801)	(35,081)	240,889
Net earnings	2,972	48,150	47,440	44,457	(24,331)	41,950	28,793	32,666	143,019	79,078	313,903
Less: Net earnings attributable to noncontrolling interests	(195)	(163)	(153)	(161)	(106)	(134)	(191)	(195)	(672)	(626)	(716)
Net earnings attributable to Kirby	$ 2,777	$ 47,987	$ 47,287	$ 44,296	$ (24,437)	$ 41,816	$ 28,602	$ 32,471	$ 142,347	$ 78,452	$ 313,187
Net earnings (loss) per share attributable to Kirby common stockholders [Abstract]
Basic (in dollars per share)	$ 0.05	$ 0.80	$ 0.79	$ 0.74	$ (0.41)	$ 0.70	$ 0.48	$ 0.54	$ 2.38	$ 1.31	$ 5.62
Diluted (in dollars per share)	$ 0.05	$ 0.80	$ 0.79	$ 0.74	$ (0.41)	$ 0.70	$ 0.48	$ 0.54	$ 2.37	$ 1.31	$ 5.62