CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) [Abstract]
Net earnings	$ 41,950	$ 28,789	$ 103,409	$ 82,406
Other comprehensive income (loss), net of taxes:
Pension and postretirement benefits	438	507	855	15,393
Foreign currency translation adjustments	(60)	(164)	(69)	(164)
Reclassification to retained earnings of stranded tax effects from tax reform	0	0	(7,925)	0
Total other comprehensive income (loss), net of taxes	378	343	(7,139)	15,229
Total comprehensive income, net of taxes	42,328	29,132	96,270	97,635
Net earnings attributable to noncontrolling interests	(134)	(182)	(520)	(538)
Comprehensive income attributable to Kirby	$ 42,194	$ 28,950	$ 95,750	$ 97,097