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Earnings Per Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Earnings Per Share [Abstract]                      
Net earnings attributable to Kirby $ 50,688 $ 56,843 $ 58,075 $ 61,078 $ 68,051 $ 76,717 $ 74,992 $ 62,246 $ 226,684 $ 282,006 $ 253,061
Undistributed earnings allocated to restricted shares                 (1,345) (1,643) (1,819)
Income available to Kirby common stockholders - basic                 225,339 280,363 251,242
Undistributed earnings allocated to restricted shares                 1,345 1,643 1,819
Undistributed earnings reallocated to restricted shares                 (1,343) (1,637) (1,813)
Income available to Kirby common stockholders - diluted                 $ 225,341 $ 280,369 $ 251,248
Shares outstanding [Abstract]                      
Weighted average common stock issued and outstanding (in shares)                 55,056 57,006 56,762
Weighted average unvested restricted stock (in shares)                 (327) (332) (408)
Weighted average common stock outstanding - basic (in shares)                 54,729 56,674 56,354
Dilutive effect of stock options (in shares)                 97 193 198
Weighted average common stock outstanding - diluted (in shares)                 54,826 56,867 56,552
Net earnings per share attributable to Kirby common stockholders [Abstract]                      
Basic (in dollars per share) $ 0.94 $ 1.04 $ 1.04 $ 1.09 $ 1.19 $ 1.34 $ 1.32 $ 1.09 $ 4.12 $ 4.95 $ 4.46
Diluted (in dollars per share) $ 0.94 $ 1.04 $ 1.04 $ 1.09 $ 1.19 $ 1.34 $ 1.31 $ 1.09 $ 4.11 $ 4.93 $ 4.44
Antidilutive securities excluded from computation of earnings per share (in shares)                 227,000 75,000 2,000