Segment Information (Summary Of Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 551,961	$ 511,728	$ 1,586,103	$ 1,511,263
Operating Income	41,690	32,583	107,461	103,637
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues	428,619	412,673	1,261,194	1,234,442
Operating Income	39,138	27,101	98,238	85,158
Value Added Services
Segment Reporting Information [Line Items]
Revenues	106,490	96,455	292,145	270,150
Operating Income	1,022	4,193	5,132	12,295
Other Segment
Segment Reporting Information [Line Items]
Revenues	16,868	3,368	33,115	7,495
Operating Income	404	949	1,245	3,477
Corporate Segment
Segment Reporting Information [Line Items]
Revenues	688	1,021	2,075	2,667
Operating Income	1,126	340	2,846	2,707
Subtotal
Segment Reporting Information [Line Items]
Revenues	552,665	513,517	1,588,529	1,514,754
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	$ (704)	$ (1,789)	$ (2,426)	$ (3,491)