EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
EARNINGS PER SHARE [Abstract]
Net earnings attributable to Kirby	$ 63,093	$ 47,551	$ 119,671	$ 98,495
Undistributed earnings allocated to restricted shares	(459)	(375)	(859)	(769)
Income available to Kirby common stockholders - basic	62,634	47,176	118,812	97,726
Undistributed earnings allocated to restricted shares	459	375	859	769
Undistributed earnings reallocated to restricted shares	(457)	(374)	(856)	(765)
Income available to Kirby common stockholders - diluted	$ 62,636	$ 47,177	$ 118,815	$ 97,730
Shares outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	56,752,000	55,869,000	56,712,000	55,839,000
Weighted average unvested restricted stock (in shares)	(413,000)	(441,000)	(407,000)	(436,000)
Weighted average common stock outstanding - basic (in shares)	56,339,000	55,428,000	56,305,000	55,403,000
Dilutive effect of stock options (in shares)	190,000	212,000	188,000	235,000
Weighted average common stock outstanding - diluted (in shares)	56,529,000	55,640,000	56,493,000	55,638,000
Net earnings per share attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 1.11	$ 0.85	$ 2.11	$ 1.76
Diluted (in dollars per share)	$ 1.11	$ 0.85	$ 2.10	$ 1.76
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	165,000	157,000