CONDENSED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Net earnings	$ 63,004	$ 39,244	$ 160,943	$ 85,436
Other comprehensive income, net of taxes:
Pension and postretirement benefits	(61)	9,110	1,152	13,254
Foreign currency translation adjustments	143	(608)	1,073	(743)
Total other comprehensive income, net of taxes	82	8,502	2,225	12,511
Total comprehensive income, net of taxes	63,086	47,746	163,168	97,947
Net (earnings) loss attributable to noncontrolling interests	(40)	(153)	86	(454)
Comprehensive income attributable to Kirby	$ 63,046	$ 47,593	$ 163,254	$ 97,493