EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
EARNINGS PER SHARE [Abstract]
Net earnings attributable to Kirby	$ 56,843	$ 76,717	$ 175,996	$ 213,955
Undistributed earnings allocated to restricted shares	(347)	(449)	(1,044)	(1,255)
Income available to Kirby common stockholders - basic	56,496	76,268	174,952	212,700
Undistributed earnings allocated to restricted shares	347	449	1,044	1,255
Undistributed earnings reallocated to restricted shares	(347)	(447)	(1,042)	(1,250)
Income available to Kirby common stockholders - diluted	$ 56,496	$ 76,270	$ 174,954	$ 212,705
Shares Outstanding: [Abstract]
Weighted average common stock issued and outstanding (in shares)	54,721,000	57,059,000	55,414,000	56,992,000
Weighted average unvested restricted stock (in shares)	(335,000)	(334,000)	(329,000)	(334,000)
Weighted average common stock outstanding - basic (in shares)	54,386,000	56,725,000	55,085,000	56,658,000
Dilutive effect of stock options (in shares)	86,000	194,000	108,000	200,000
Weighted average common stock outstanding - diluted (in shares)	54,472,000	56,919,000	55,193,000	56,858,000
Net earnings per share attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 1.04	$ 1.34	$ 3.18	$ 3.75
Diluted (in dollars per share)	$ 1.04	$ 1.34	$ 3.17	$ 3.74
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)			227,000	46,000