Segment Information (Summary Of Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 646,365	$ 629,735	$ 619,130	$ 562,684	$ 567,365	$ 528,643	$ 519,508	$ 501,221	$ 2,457,914	$ 2,116,737	$ 2,008,991
Operating income	$ 74,931	$ 63,386	$ 50,783	$ 35,115	$ 45,061	$ 35,874	$ 36,913	$ 25,972	224,215	143,820	126,070
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues									1,881,323	1,635,244	1,533,981
Operating income									202,581	138,059	107,713
Werner Logistics
Segment Reporting Information [Line Items]
Revenues									518,078	417,639	417,172
Operating income									20,378	8,683	20,734
Other
Segment Reporting Information [Line Items]
Revenues									56,903	62,745	57,062
Operating income									(453)	35	(6,177)
Corporate
Segment Reporting Information [Line Items]
Revenues									2,759	1,938	1,749
Operating income									1,709	(2,957)	3,800
Subtotal
Segment Reporting Information [Line Items]
Revenues									2,459,063	2,117,566	2,009,964
Inter-segment eliminations
Segment Reporting Information [Line Items]
Revenues									$ (1,149)	$ (829)	$ (973)