Segment Information (Summary Of Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Reporting Information [Line Items]
Revenues	$ 521,812	$ 515,897	$ 1,020,188	$ 985,326
Operating Income	51,113	46,767	86,515	74,209
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues	432,888	439,944	850,378	842,290
Operating Income	45,074	44,764	76,438	69,030
Value Added Services
Segment Reporting Information [Line Items]
Revenues	84,024	71,227	160,778	134,800
Operating Income	4,302	3,719	8,288	7,129
Other Segment
Segment Reporting Information [Line Items]
Revenues	3,481	3,234	6,538	5,911
Operating Income	855	(1,903)	1,359	(1,622)
Corporate Segment
Segment Reporting Information [Line Items]
Revenues	1,419	1,492	2,494	2,325
Operating Income	$ 882	$ 187	$ 430	$ (328)