Segment Information (Summary Of Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Revenues	$ 506,504	$ 509,587	$ 1,526,692	$ 1,494,913
Operating Income	41,805	50,066	128,320	124,275
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues	420,003	428,565	1,270,381	1,270,855
Operating Income	36,659	45,715	113,097	114,745
Value Added Services
Segment Reporting Information [Line Items]
Revenues	82,490	76,635	243,268	211,435
Operating Income	3,779	4,074	12,067	11,203
Other Segment
Segment Reporting Information [Line Items]
Revenues	2,872	3,274	9,410	9,185
Operating Income	402	545	1,761	(1,077)
Corporate Segment
Segment Reporting Information [Line Items]
Revenues	1,139	1,113	3,633	3,438
Operating Income	$ 965	$ (268)	$ 1,395	$ (596)