CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) [Abstract]
Net earnings	$ 32,666	$ 27,645
Other comprehensive income (loss), net of taxes:
Pension and postretirement benefits	430	746
Foreign currency translation adjustments	420	0
Reclassification to retained earnings of stranded tax effects from tax reform	(7,925)	0
Total other comprehensive income (loss), net of taxes	(7,075)	746
Total comprehensive income, net of taxes	25,591	28,391
Net earnings attributable to noncontrolling interests	(195)	(162)
Comprehensive income attributable to Kirby	$ 25,396	$ 28,229