EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
EARNINGS PER SHARE [Abstract]
Net earnings attributable to Kirby	$ 58,075	$ 74,992	$ 119,153	$ 137,238
Undistributed earnings allocated to restricted shares	(350)	(435)	(696)	(806)
Income available to Kirby common stockholders - basic	57,725	74,557	118,457	136,432
Undistributed earnings allocated to restricted shares	350	435	696	806
Undistributed earnings reallocated to restricted shares	(349)	(434)	(695)	(803)
Income available to Kirby common stockholders - diluted	$ 57,726	$ 74,558	$ 118,458	$ 136,435
Shares Outstanding: [Abstract]
Weighted average common stock issued and outstanding (in shares)	55,651,000	57,010,000	55,772,000	56,957,000
Weighted average unvested restricted stock (in shares)	(336,000)	(331,000)	(326,000)	(334,000)
Weighted average common stock outstanding - basic (in shares)	55,315,000	56,679,000	55,446,000	56,623,000
Dilutive effect of stock options (in shares)	117,000	190,000	119,000	203,000
Weighted average common stock outstanding - diluted (in shares)	55,432,000	56,869,000	55,565,000	56,826,000
Net earnings per share attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 1.04	$ 1.32	$ 2.14	$ 2.41
Diluted (in dollars per share)	$ 1.04	$ 1.31	$ 2.13	$ 2.40
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)			185,000	117,000