CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Net earnings (loss)	$ (271,592)	$ 143,019	$ 79,078
Other comprehensive loss, net of taxes:
Pension and postretirement benefits	(23,320)	(4,203)	7,638
Foreign currency translation adjustments	(333)	(85)	(819)
Reclassification to retained earnings of stranded tax effects from tax reform	0	0	(7,925)
Total other comprehensive loss, net of taxes	(23,653)	(4,288)	(1,106)
Total comprehensive income (loss), net of taxes	(295,245)	138,731	77,972
Net earnings attributable to noncontrolling interests	(954)	(672)	(626)
Comprehensive income (loss) attributable to Kirby	$ (296,199)	$ 138,059	$ 77,346