Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Net Income (Loss) Attributable to Parent [Abstract]
Net earnings (loss) attributable to Kirby	$ (347,241)	$ 44,296
Undistributed earnings allocated to restricted shares	0	(119)
Income (loss) available to Kirby common stockholders - basic	(347,241)	44,177
Undistributed earnings allocated to restricted shares	0	119
Undistributed earnings reallocated to restricted shares	0	(119)
Income (loss) available to Kirby common stockholders - diluted	$ (347,241)	$ 44,177
Shares outstanding [Abstract]
Weighted average common stock issued and outstanding (in shares)	59,983,000	59,869,000
Weighted average unvested restricted stock (in shares)	(100,000)	(160,000)
Weighted average common stock outstanding - basic (in shares)	59,883,000	59,709,000
Dilutive effect of stock options and restricted stock units (in shares)	0	114,000
Weighted average common stock outstanding - diluted (in shares)	59,883,000	59,823,000
Net earnings (loss) per share attributable to Kirby common stockholders:
Basic (in dollars per share)	$ (5.80)	$ 0.74
Diluted (in dollars per share)	$ (5.80)	$ 0.74
Antidilutive securities excluded from computation of earnings per share (in shares)	681,000	479,000
RSUs [Member]
Net earnings (loss) per share attributable to Kirby common stockholders:
Antidilutive securities excluded from computation of earnings per share (in shares)	344,000	1,000