Segment Information (Summary Of Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Revenues	$ 511,728	$ 506,504	$ 1,511,263	$ 1,526,692
Operating Income	32,583	41,805	103,637	128,320
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues	412,673	420,003	1,234,442	1,270,381
Operating Income	27,101	36,659	85,158	113,097
Value Added Services
Segment Reporting Information [Line Items]
Revenues	96,455	83,213	270,150	245,839
Operating Income	4,193	3,779	12,295	12,067
Other Segment
Segment Reporting Information [Line Items]
Revenues	3,368	2,872	7,495	9,410
Operating Income	949	402	3,477	1,761
Corporate Segment
Segment Reporting Information [Line Items]
Revenues	1,021	1,139	2,667	3,633
Operating Income	340	965	2,707	1,395
Subtotal
Segment Reporting Information [Line Items]
Revenues	513,517	507,227	1,514,754	1,529,263
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	$ (1,789)	$ (723)	$ (3,491)	$ (2,571)