EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
EARNINGS PER SHARE [Abstract]
Net earnings attributable to Kirby	$ 76,717	$ 69,123	$ 213,955	$ 188,794
Undistributed earnings allocated to restricted shares	(449)	(504)	(1,255)	(1,363)
Income available to Kirby common stockholders - basic	76,268	68,619	212,700	187,431
Undistributed earnings allocated to restricted shares	449	504	1,255	1,363
Undistributed earnings reallocated to restricted shares	(447)	(502)	(1,250)	(1,358)
Income available to Kirby common stockholders - diluted	$ 76,270	$ 68,621	$ 212,705	$ 187,436
Weighted average common stock issued and outstanding (in shares)	57,059,000	56,789,000	56,992,000	56,738,000
Weighted average unvested restricted stock (in shares)	(334,000)	(414,000)	(334,000)	(409,000)
Weighted average common stock outstanding - basic (in shares)	56,725,000	56,375,000	56,658,000	56,329,000
Dilutive effect of stock options (in shares)	194,000	197,000	200,000	191,000
Weighted average common stock outstanding - diluted (in shares)	56,919,000	56,572,000	56,858,000	56,520,000
Net earnings per share attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 1.34	$ 1.22	$ 3.75	$ 3.33
Diluted (in dollars per share)	$ 1.34	$ 1.21	$ 3.74	$ 3.32
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)			46,000	112,000