EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
EARNINGS PER SHARE [Abstract]
Net earnings attributable to Kirby	$ 69,123	$ 53,055	$ 188,794	$ 151,550
Undistributed earnings allocated to restricted shares	(504)	(409)	(1,363)	(1,180)
Income available to Kirby common stockholders - basic	68,619	52,646	187,431	150,370
Undistributed earnings allocated to restricted shares	504	409	1,363	1,180
Undistributed earnings reallocated to restricted shares	(502)	(407)	(1,358)	(1,175)
Income available to Kirby common stockholders - diluted	$ 68,621	$ 52,648	$ 187,436	$ 150,375
Shares outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	56,789,000	55,875,000	56,738,000	55,851,000
Weighted average unvested restricted stock (in shares)	(414,000)	(430,000)	(409,000)	(435,000)
Weighted average common stock outstanding - basic (in shares)	56,375,000	55,445,000	56,329,000	55,416,000
Dilutive effect of stock options (in shares)	197,000	182,000	191,000	218,000
Weighted average common stock outstanding - diluted (in shares)	56,572,000	55,627,000	56,520,000	55,634,000
Net earnings per share attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 1.22	$ 0.95	$ 3.33	$ 2.71
Diluted (in dollars per share)	$ 1.21	$ 0.95	$ 3.32	$ 2.70
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)			112,000	156,000