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Segment Information (Summary Of Segment Information) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 567,365 | $ 528,643 | $ 519,508 | $ 501,221 | $ 518,832 | $ 508,676 | $ 498,681 | $ 482,802 | $ 2,116,737 | $ 2,008,991 | $ 2,093,529
Operating income | $ 45,061 | $ 35,874 | $ 36,913 | $ 25,972 | $ 34,956 | $ 29,074 | $ 29,553 | $ 32,487 | 143,820 | 126,070 | 200,456
Truckload Transportation Services |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,635,244 | 1,533,981 | 1,644,874
Operating income |  |  |  |  |  |  |  |  | 138,059 | 107,713 | 189,850
Werner Logistics |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 417,639 | 417,172 | 393,174
Operating income |  |  |  |  |  |  |  |  | 8,683 | 20,734 | 16,898
Other |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 62,745 | 57,062 | 54,512
Operating income |  |  |  |  |  |  |  |  | 35 | (6,177) | (7,513)
Corporate |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,938 | 1,749 | 2,297
Operating income |  |  |  |  |  |  |  |  | (2,957) | 3,800 | 1,221
Subtotal |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 2,117,566 | 2,009,964 | 2,094,857
Inter-segment eliminations |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | $ (829) | $ (973) | $ (1,328)

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