Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share [Abstract]
Net earnings attributable to Kirby	$ 57,888	$ 53,055	$ 47,551	$ 50,944	$ 56,170	$ 52,734	$ 41,692	$ 32,430	$ 209,438	$ 183,026	$ 116,249
Undistributed earnings allocated to restricted shares									(1,618)	(1,613)	(1,125)
Income available to Kirby common stockholders - basic									207,820	181,413	115,124
Undistributed earnings allocated to restricted shares									1,618	1,613	1,125
Undistributed earnings reallocated to restricted shares									(1,612)	(1,606)	(1,122)
Income available to Kirby common stockholders - diluted									$ 207,826	$ 181,420	$ 115,127
Weighted average common stock issued and outstanding (in shares)									55,897,000	54,673,000	53,852,000
Weighted average unvested restricted stock (in shares)									(431,000)	(482,000)	(521,000)
Weighted average common stock outstanding - basic (in shares)									55,466,000	54,191,000	53,331,000
Dilutive effect of stock options (in shares)									208,000	222,000	135,000
Weighted average common stock outstanding - diluted (in shares)									55,674,000	54,413,000	53,466,000
Net earnings per share attributable to Kirby common stockholders [Abstract]
Basic (in dollars per share)	$ 1.03	$ 0.95	$ 0.85	$ 0.91	$ 1.01	$ 0.95	$ 0.78	$ 0.60	$ 3.75	$ 3.35	$ 2.16
Diluted (in dollars per share)	$ 1.03	$ 0.95	$ 0.85	$ 0.91	$ 1.00	$ 0.94	$ 0.77	$ 0.60	$ 3.73	$ 3.33	$ 2.15
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)									100,000	2,000	114,000