CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Noncontrolling Interests [Member]	Total
Cumulative effect of adoption of ASU 2016-09				$ 0
Balance at beginning of year at Dec. 31, 2014	$ 5,978	$ 428,475	$ (61,037)	1,974,146	$ (93,526)	$ 10,877
Issuance of shares in acquisition	0	0
Excess (deficit) of proceeds received upon exercise of stock options and issuance of restricted stock over cost of treasury stock issued		3,530
Tax benefit (expense) realized from equity compensation plans		964
Issuance of restricted stock, net of forfeitures		(9,290)
Amortization of unearned compensation		11,104
Acquisitions of noncontrolling interests		0				0
Net earnings attributable to Kirby for the year				226,684			$ 226,684
Purchase of treasury stock (35,000 in 2016 and 3,316,000 in 2015)					(241,105)
Cost of treasury stock issued upon exercise of stock options and issuance of restricted stock (138,000 in 2017, 170,000 in 2016 and 166,000 in 2015)					6,537
Net earnings attributable to noncontrolling interests						1,286	1,286
Return of investment to noncontrolling interests						(1,778)	1,778
Other comprehensive income (loss), net of taxes			16,351				16,351
Balance at end of year at Dec. 31, 2015	5,978	434,783	(44,686)	2,200,830	(328,094)	10,385
Cumulative effect of adoption of ASU 2016-09				0
Issuance of shares in acquisition	0	0
Excess (deficit) of proceeds received upon exercise of stock options and issuance of restricted stock over cost of treasury stock issued		(755)
Tax benefit (expense) realized from equity compensation plans		(824)
Issuance of restricted stock, net of forfeitures		(10,218)
Amortization of unearned compensation		11,675
Acquisitions of noncontrolling interests		(2,202)				(6,258)
Net earnings attributable to Kirby for the year				141,406			141,406
Purchase of treasury stock (35,000 in 2016 and 3,316,000 in 2015)					(1,827)
Cost of treasury stock issued upon exercise of stock options and issuance of restricted stock (138,000 in 2017, 170,000 in 2016 and 166,000 in 2015)					9,573
Net earnings attributable to noncontrolling interests						1,398	1,398
Return of investment to noncontrolling interests						(1,976)	1,976
Other comprehensive income (loss), net of taxes			(6,321)				(6,321)
Balance at end of year at Dec. 31, 2016	5,978	432,459	(51,007)	2,342,236	(320,348)	3,549	2,412,867
Cumulative effect of adoption of ASU 2016-09 | ASU 2016-09 [Member]				(8,486)			8,486
Issuance of shares in acquisition	569	365,985
Excess (deficit) of proceeds received upon exercise of stock options and issuance of restricted stock over cost of treasury stock issued		833
Tax benefit (expense) realized from equity compensation plans		0
Issuance of restricted stock, net of forfeitures		(7,770)
Amortization of unearned compensation		11,460
Acquisitions of noncontrolling interests		(6)				0
Net earnings attributable to Kirby for the year				313,187			313,187
Purchase of treasury stock (35,000 in 2016 and 3,316,000 in 2015)					0
Cost of treasury stock issued upon exercise of stock options and issuance of restricted stock (138,000 in 2017, 170,000 in 2016 and 166,000 in 2015)					7,128
Net earnings attributable to noncontrolling interests						716	716
Return of investment to noncontrolling interests						(862)	862
Other comprehensive income (loss), net of taxes			18,602				18,602
Balance at end of year at Dec. 31, 2017	$ 6,547	$ 802,961	$ (32,405)	$ 2,646,937	$ (313,220)	$ 3,403	$ 3,114,223