EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
EARNINGS PER SHARE [Abstract]
Net earnings attributable to Kirby	$ 32,010	$ 56,843	$ 109,051	$ 175,996
Undistributed earnings allocated to restricted shares	(239)	(347)	(766)	(1,044)
Income available to Kirby common stockholders - basic	31,771	56,496	108,285	174,952
Undistributed earnings allocated to restricted shares	239	347	766	1,044
Undistributed earnings reallocated to restricted shares	(238)	(347)	(765)	(1,042)
Income available to Kirby common stockholders - diluted	$ 31,772	$ 56,496	$ 108,286	$ 174,954
Shares Outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	53,856,000	54,721,000	53,827,000	55,414,000
Weighted average unvested restricted stock (in shares)	(401,000)	(335,000)	(378,000)	(329,000)
Weighted average common stock outstanding - basic (in shares)	53,455,000	54,386,000	53,449,000	55,085,000
Dilutive effect of stock options (in shares)	46,000	86,000	54,000	108,000
Weighted average common stock outstanding - diluted (in shares)	53,501,000	54,472,000	53,503,000	55,193,000
Net earnings per share attributable to Kirby common stockholders [Abstract]
Basic (in dollars per share)	$ 0.59	$ 1.04	$ 2.03	$ 3.18
Diluted (in dollars per share)	$ 0.59	$ 1.04	$ 2.02	$ 3.17
Antidilutive securities excluded from computation of earnings per share (in shares)			520,000	227,000