CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) [Abstract]
Net earnings	$ 44,457	$ 32,666
Other comprehensive income (loss), net of taxes:
Pension and postretirement benefits	411	430
Foreign currency translation adjustments	129	420
Reclassification to retained earnings of stranded tax effects from tax reform	0	(7,925)
Total other comprehensive income (loss), net of taxes	540	(7,075)
Total comprehensive income, net of taxes	44,997	25,591
Net earnings attributable to noncontrolling interests	(161)	(195)
Comprehensive income attributable to Kirby	$ 44,836	$ 25,396