Segment Information (Summary Of Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues	$ 620,302	$ 590,214	$ 568,959	$ 592,703	$ 621,787	$ 618,264	$ 627,533	$ 596,117	$ 2,372,178	$ 2,463,701	$ 2,457,914
Operating income	$ 81,451	$ 62,103	$ 52,818	$ 31,066	$ 65,654	$ 53,357	$ 58,442	$ 48,019	227,438	225,472	224,215
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues									1,843,209	1,909,776	1,881,323
Operating income									222,007	202,660	202,581
Werner Logistics
Segment Reporting Information [Line Items]
Revenues									469,791	489,729	518,078
Operating income									6,005	16,288	20,378
Other
Segment Reporting Information [Line Items]
Revenues									57,276	61,850	56,903
Operating income									3,839	5,535	(453)
Corporate
Segment Reporting Information [Line Items]
Revenues									2,009	2,589	2,759
Operating income									(4,413)	989	1,709
Subtotal
Segment Reporting Information [Line Items]
Revenues									2,372,285	2,463,944	2,459,063
Inter-segment eliminations
Segment Reporting Information [Line Items]
Revenues									$ (107)	$ (243)	$ (1,149)