CONDENSED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Statement of Comprehensive Income [Abstract]
Net earnings	$ 57,318	$ 28,606	$ 97,939	$ 46,192
Other comprehensive income, net of taxes:
Pension and postretirement benefits	1,274	4,131	1,213	4,144
Foreign currency translation adjustments	705	(611)	930	(135)
Total other comprehensive income, net of taxes	1,979	3,520	2,143	4,009
Total comprehensive income, net of taxes	59,297	32,126	100,082	50,201
Net (earnings) loss attributable to noncontrolling interests	49	(149)	126	(301)
Comprehensive income attributable to Kirby	$ 59,346	$ 31,977	$ 100,208	$ 49,900