Revenue (Disaggregation of Revenue by Revenue Source) (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
Disaggregation of revenue
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
Truckload Transportation Services
Disaggregation of revenue
Revenues									1,909,776	1,881,323	1,635,244
Werner Logistics
Disaggregation of revenue
Revenues									489,729	518,078	417,639
Inter-segment eliminations
Disaggregation of revenue
Revenues									(243)	(1,149)	(829)
Transportation Services
Disaggregation of revenue
Revenues									2,399,262	2,398,252	2,052,054
Other revenues
Disaggregation of revenue
Revenues									$ 64,439	$ 59,662	$ 64,683