EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
EARNINGS PER SHARE [Abstract]
Net earnings attributable to Kirby	$ 27,483	$ 38,099
Undistributed earnings allocated to restricted shares	(190)	(240)
Income available to Kirby common stockholders - basic	27,293	37,859
Undistributed earnings allocated to restricted shares	190	240
Undistributed earnings reallocated to restricted shares	(189)	(239)
Income available to Kirby common stockholders - diluted	$ 27,294	$ 37,860
Shares Outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	53,914	53,780
Weighted average unvested restricted stock (in shares)	(372)	(338)
Weighted average common stock outstanding - basic (in shares)	53,542	53,442
Dilutive effect of stock options (in shares)	67	41
Weighted average common stock outstanding - diluted (in shares)	53,609	53,483
Net earnings per share attributable to Kirby common stockholders [Abstract]
Basic (in dollars per share)	$ 0.51	$ 0.71
Diluted (in dollars per share)	$ 0.51	$ 0.71
Antidilutive securities excluded from computation of earnings per share (in shares)	487	542