Revenue (Disaggregation of Revenue by Revenue Source) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of revenue
Revenues	$ 646,365	$ 629,735	$ 619,130	$ 562,684	$ 567,365	$ 528,643	$ 519,508	$ 501,221	$ 2,457,914	$ 2,116,737	$ 2,008,991
Truckload Transportation Services
Disaggregation of revenue
Revenues									1,881,323	1,635,244	1,533,981
Werner Logistics
Disaggregation of revenue
Revenues									518,078	417,639	417,172
Inter-segment eliminations
Disaggregation of revenue
Revenues									(1,149)	(829)	(973)
Transportation Services
Disaggregation of revenue
Revenues									2,398,252	2,052,054	1,950,180
Other revenues
Disaggregation of revenue
Revenues									$ 59,662	$ 64,683	$ 58,811