EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
EARNINGS PER SHARE [Abstract]
Net earnings attributable to Kirby	$ 56,578	$ 50,944
Undistributed earnings allocated to restricted shares	(401)	(393)
Income available to Kirby common stockholders - basic	56,177	50,551
Undistributed earnings allocated to restricted shares	401	393
Undistributed earnings reallocated to restricted shares	(399)	(391)
Income available to Kirby common stockholders - diluted	$ 56,179	$ 50,553
Shares outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	56,669,000	55,808,000
Weighted average unvested restricted stock (in shares)	(401,000)	(430,000)
Weighted average common stock outstanding - basic (in shares)	56,268,000	55,378,000
Dilutive effect of stock options (in shares)	187,000	257,000
Weighted average common stock outstanding - diluted (in shares)	56,455,000	55,635,000
Net earnings per share attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 1.00	$ 0.91
Diluted (in dollars per share)	$ 1.00	$ 0.91
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	209,000	102,000