CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) [Abstract]
Net earnings	$ 28,793	$ 25,972	$ 61,459	$ 53,617
Other comprehensive income (loss), net of taxes:
Pension and postretirement benefits	(13)	14,140	417	14,886
Foreign currency translation adjustments	(429)	0	(9)	0
Reclassification to retained earnings of stranded tax effects from tax reform	0	0	(7,925)	0
Total other comprehensive income (loss), net of taxes	(442)	14,140	(7,517)	14,886
Total comprehensive income, net of taxes	28,351	40,112	53,942	68,503
Net earnings attributable to noncontrolling interests	(191)	(194)	(386)	(356)
Comprehensive income attributable to Kirby	$ 28,160	$ 39,918	$ 53,556	$ 68,147