Segment Information (Summary Of Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 492,887	$ 498,376
Operating Income	28,693	35,402
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues	408,900	417,490
Operating Income	23,615	31,364
Value Added Services
Segment Reporting Information [Line Items]
Revenues	82,510	77,517
Operating Income	3,613	3,986
Other Segment
Segment Reporting Information [Line Items]
Revenues	2,044	3,057
Operating Income	905	504
Corporate Segment
Segment Reporting Information [Line Items]
Revenues	650	1,075
Operating Income	560	(452)
Subtotal
Segment Reporting Information [Line Items]
Revenues	494,104	499,139
Intersegment Elimination
Segment Reporting Information [Line Items]
Revenues	$ (1,217)	$ (763)