Revenue (Disaggregation of Revenue by Revenue Source) (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
Disaggregation of revenue
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
Truckload Transportation Services
Disaggregation of revenue
Revenues									1,843,209	1,909,776	1,881,323
Werner Logistics
Disaggregation of revenue
Revenues									469,791	489,729	518,078
Inter-segment eliminations
Disaggregation of revenue
Revenues									(107)	(243)	(1,149)
Transportation Services
Disaggregation of revenue
Revenues									2,312,893	2,399,262	2,398,252
Other revenues
Disaggregation of revenue
Revenues									$ 59,285	$ 64,439	$ 59,662