Segment Information (Summary Of Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Revenues	$ 506,648	$ 521,812	$ 999,535	$ 1,020,188
Operating Income	42,361	51,113	71,054	86,515
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues	412,869	432,888	821,769	850,378
Operating Income	34,442	45,074	58,057	76,438
Value Added Services
Segment Reporting Information [Line Items]
Revenues	91,185	85,109	173,695	162,626
Operating Income	4,489	4,302	8,102	8,288
Other Segment
Segment Reporting Information [Line Items]
Revenues	2,083	3,481	4,127	6,538
Operating Income	1,623	855	2,528	1,359
Corporate Segment
Segment Reporting Information [Line Items]
Revenues	996	1,419	1,646	2,494
Operating Income	1,807	882	2,367	430
Subtotal
Segment Reporting Information [Line Items]
Revenues	507,133	522,897	1,001,237	1,022,036
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	$ (485)	$ (1,085)	$ (1,702)	$ (1,848)