CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Net earnings	$ 313,903	$ 142,804	$ 227,970
Other comprehensive income (loss), net of taxes:
Pension and postretirement benefits	18,748	(6,321)	16,322
Foreign currency translation adjustments	(146)	0	29
Total other comprehensive income (loss), net of taxes	18,602	(6,321)	16,351
Total comprehensive income, net of taxes	332,505	136,483	244,321
Net earnings attributable to noncontrolling interests	(716)	(1,398)	(1,286)
Comprehensive income attributable to Kirby	$ 331,789	$ 135,085	$ 243,035