Segment Information (Summary Of Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Segment Reporting Information [Line Items]
Revenues	$ 498,376	$ 469,429
Operating Income	35,402	27,442
Truckload Transportation Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues	417,490	402,346
Operating Income	31,364	24,266
Value Added Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues	76,754	63,573
Operating Income	3,986	3,410
Other Segment [Member]
Segment Reporting Information [Line Items]
Revenues	3,057	2,677
Operating Income	504	281
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Revenues	1,075	833
Operating Income	$ (452)	$ (515)