CONDENSED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
CONDENSED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Net earnings (loss)	$ (265,152)	$ 27,693	$ (257,920)	$ (294,007)
Other comprehensive income (loss), net of taxes:
Pension and postretirement benefits	3,142	(4,279)	7,494	(6,674)
Foreign currency translation adjustments	(122)	(239)	(705)	(1,162)
Total other comprehensive income (loss), net of taxes	3,020	(4,518)	6,789	(7,836)
Total comprehensive income (loss), net of taxes	(262,132)	23,175	(251,131)	(301,843)
Net (earnings) loss attributable to noncontrolling interests	422	(204)	5	(743)
Comprehensive income (loss) attributable to Kirby	$ (261,710)	$ 22,971	$ (251,126)	$ (302,586)