Revenue (Disaggregation of Revenue by Revenue Source) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of revenue
Revenues	$ 619,130	$ 519,508	$ 1,181,814	$ 1,020,729
Truckload Transportation Services
Disaggregation of revenue
Revenues	470,277	403,502	901,833	788,505
Werner Logistics
Disaggregation of revenue
Revenues	134,012	100,804	251,432	200,657
Inter-segment eliminations
Disaggregation of revenue
Revenues	(212)	(449)	(670)	(616)
Transportation Services
Disaggregation of revenue
Revenues	604,077	503,857	1,152,595	988,546
Other revenues
Disaggregation of revenue
Revenues	$ 15,053	$ 15,651	$ 29,219	$ 32,183