CONDENSED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Statement of Comprehensive Income [Abstract]
Net earnings	$ 83,982	$ 57,318	$ 153,897	$ 97,939
Other comprehensive income, net of taxes:
Pension and postretirement benefits	986	1,274	591	1,213
Foreign currency translation adjustments	(473)	705	(473)	930
Total other comprehensive income, net of taxes	513	1,979	118	2,143
Total comprehensive income, net of taxes	84,495	59,297	154,015	100,082
Net (earnings) loss attributable to noncontrolling interests	(128)	49	25	126
Comprehensive income attributable to Kirby	$ 84,367	$ 59,346	$ 154,040	$ 100,208