Summary of Significant Accounting Policies, Accounting Standards (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements [Abstract]
Operating expense	$ (19,241)	$ 67,957	$ 55,853	$ 50,720	$ (52,600)	$ 52,929	$ 47,252	$ 46,044	$ 155,289	$ 93,625	$ 247,370
Nonoperating expense	(1,140)	(1,454)	(1,541)	(1,591)	(902)	(320)	(228)	589
Statements of earnings [Abstract]
Revenues									2,970,697	2,214,418	1,770,673
Costs of sales and operating expenses									2,160,946	1,558,098	1,124,666
Operating income	(19,241)	67,957	55,853	50,720	(52,600)	52,929	47,252	46,044	155,289	93,625	247,370
Earnings before taxes on income	(30,292)	57,066	44,854	42,531	(58,860)	47,861	43,015	40,998	114,159	73,014	227,746
Provision for taxes on income	5,961	(15,116)	(16,061)	(9,865)	290,357	(19,072)	(17,043)	(13,353)	(35,081)	240,889	(84,942)
Net earnings attributable to Kirby	(24,437)	41,816	28,602	32,471	231,319	28,607	25,778	27,483	78,452	313,187	141,406
Statements of comprehensive income [Abstract]
Net earnings	(24,331)	41,950	28,793	32,666	231,497	28,789	25,972	27,645	79,078	313,903	142,804
Comprehensive income attributable to Kirby									77,346	331,789	135,085
Statements of cash flows [Abstract]
Net earnings	(24,331)	$ 41,950	$ 28,793	$ 32,666	231,497	$ 28,789	$ 25,972	$ 27,645	79,078	313,903	142,804
Provision for deferred income taxes									34,881	(256,263)	51,296
Decrease in cash flows resulting from changes in: [Abstract]
Accounts receivable									12,511	(60,405)	(12,750)
Inventory									(144,685)	19,673	3,182
Accrued and other liabilities									30,712	(3,105)	16,051
Balance sheets [Abstract]
Trade receivables	417,644				452,222				417,644	452,222
Inventories - net	507,441				315,729				507,441	315,729
Total assets	5,871,594				5,127,427				5,871,594	5,127,427	4,289,895
Deferred revenues	80,123				48,347				80,123	48,347
Deferred income taxes	542,785				468,451				542,785	468,451
Retained earnings	2,723,592				2,646,937				2,723,592	2,646,937
Total liabilities and equity	5,871,594				5,127,427				5,871,594	5,127,427
Distribution and Services [Member]
Statements of earnings [Abstract]
Revenues									1,487,554	890,312	298,780
Retained Earnings [Member]
Statements of earnings [Abstract]
Net earnings attributable to Kirby									78,452	313,187	141,406
ASU 2016-09 [Member] | Retained Earnings [Member]
New Accounting Pronouncements [Abstract]
Cumulative effect on retained earnings					0					0	8,486	$ 0
ASU 2018-02 [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
New Accounting Pronouncements [Abstract]
Cumulative effect on retained earnings					7,925					7,925	0	0
Reclassification from AOCI to retained earnings	(7,925)								(7,925)
ASU 2018-02 [Member] | Retained Earnings [Member]
New Accounting Pronouncements [Abstract]
Cumulative effect on retained earnings					(7,925)					(7,925)	0	0
Reclassification from AOCI to retained earnings	7,925								7,925
ASU 2017-07 [Member]
New Accounting Pronouncements [Abstract]
Operating expense										(621)	(2,175)
Nonoperating expense										(621)	(2,175)
Statements of earnings [Abstract]
Operating income										(621)	(2,175)
ASC 606 [Member]
New Accounting Pronouncements [Abstract]
Cumulative effect on retained earnings	(9,722)								(9,722)
ASC 606 [Member] | Balances without Adoption of ASC 606 [Member]
New Accounting Pronouncements [Abstract]
Operating expense									163,189
Statements of earnings [Abstract]
Costs of sales and operating expenses									2,181,046
Operating income									163,189
Earnings before taxes on income									122,059
Provision for taxes on income									(37,187)
Net earnings attributable to Kirby									84,246
Statements of comprehensive income [Abstract]
Net earnings									84,872
Comprehensive income attributable to Kirby									83,140
Statements of cash flows [Abstract]
Net earnings									84,872
Provision for deferred income taxes									32,775
Decrease in cash flows resulting from changes in: [Abstract]
Accounts receivable									(71,624)
Inventory									(71,985)
Accrued and other liabilities									38,459
Balance sheets [Abstract]
Trade receivables	501,779								501,779
Inventories - net	434,741								434,741
Total assets	5,883,029								5,883,029
Deferred revenues	70,858								70,858
Deferred income taxes	547,991								547,991
Retained earnings	2,739,086								2,739,086
Total liabilities and equity	5,883,029								5,883,029
ASC 606 [Member] | Balances without Adoption of ASC 606 [Member] | Distribution and Services [Member]
Statements of earnings [Abstract]
Revenues									1,515,554
ASC 606 [Member] | Effect of Change [Member]
New Accounting Pronouncements [Abstract]
Operating expense									(7,900)
Statements of earnings [Abstract]
Costs of sales and operating expenses									(20,100)
Operating income									(7,900)
Earnings before taxes on income									(7,900)
Provision for taxes on income									2,106
Net earnings attributable to Kirby									(5,794)
Statements of comprehensive income [Abstract]
Net earnings									(5,794)
Comprehensive income attributable to Kirby									(5,794)
Statements of cash flows [Abstract]
Net earnings									(5,794)
Provision for deferred income taxes									2,106
Decrease in cash flows resulting from changes in: [Abstract]
Accounts receivable									84,135
Inventory									(72,700)
Accrued and other liabilities									(7,747)
Balance sheets [Abstract]
Trade receivables	(84,135)								(84,135)
Inventories - net	72,700								72,700
Total assets	(11,435)								(11,435)
Deferred revenues	9,265								9,265
Deferred income taxes	(5,206)								(5,206)
Retained earnings	(15,494)								(15,494)
Total liabilities and equity	(11,435)								(11,435)
ASC 606 [Member] | Effect of Change [Member] | Distribution and Services [Member]
Statements of earnings [Abstract]
Revenues									(28,000)
ASC 606 [Member] | Retained Earnings [Member]
New Accounting Pronouncements [Abstract]
Cumulative effect on retained earnings	(9,722)				$ 9,722				(9,722)	$ 9,722	$ 0	$ 0
ASU 2016-02 [Member]
New Accounting Pronouncements [Abstract]
Right-of-use assets	185,000								185,000
Liabilities for operating leases	$ 180,000								$ 180,000