Segment Information (Summary Of Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 567,365	$ 528,643	$ 519,508	$ 501,221	$ 518,832	$ 508,676	$ 498,681	$ 482,802	$ 2,116,737	$ 2,008,991	$ 2,093,529
Operating income	$ 45,061	$ 35,874	$ 36,913	$ 25,972	$ 34,956	$ 29,074	$ 29,553	$ 32,487	143,820	126,070	200,456
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues									1,635,244	1,533,981	1,644,874
Operating income									138,059	107,713	189,850
Werner Logistics
Segment Reporting Information [Line Items]
Revenues									417,639	417,172	393,174
Operating income									8,683	20,734	16,898
Other
Segment Reporting Information [Line Items]
Revenues									62,745	57,062	54,512
Operating income									35	(6,177)	(7,513)
Corporate
Segment Reporting Information [Line Items]
Revenues									1,938	1,749	2,297
Operating income									(2,957)	3,800	1,221
Subtotal
Segment Reporting Information [Line Items]
Revenues									2,117,566	2,009,964	2,094,857
Inter-segment eliminations
Segment Reporting Information [Line Items]
Revenues									$ (829)	$ (973)	$ (1,328)