Segment Information (Summary Of Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 621,787	$ 618,264	$ 627,533	$ 596,117	$ 646,365	$ 629,735	$ 619,130	$ 562,684	$ 2,463,701	$ 2,457,914	$ 2,116,737
Operating income	$ 65,654	$ 53,357	$ 58,442	$ 48,019	$ 74,931	$ 63,386	$ 50,783	$ 35,115	225,472	224,215	143,820
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues									1,909,776	1,881,323	1,635,244
Operating income									202,660	202,581	138,059
Werner Logistics
Segment Reporting Information [Line Items]
Revenues									489,729	518,078	417,639
Operating income									16,288	20,378	8,683
Other
Segment Reporting Information [Line Items]
Revenues									61,850	56,903	62,745
Operating income									5,535	(453)	35
Corporate
Segment Reporting Information [Line Items]
Revenues									2,589	2,759	1,938
Operating income									989	1,709	(2,957)
Subtotal
Segment Reporting Information [Line Items]
Revenues									2,463,944	2,459,063	2,117,566
Inter-segment eliminations
Segment Reporting Information [Line Items]
Revenues									$ (243)	$ (1,149)	$ (829)