Segment Information (Summary Of Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenues	$ 517,920	$ 511,728	$ 506,648	$ 492,887	$ 509,694	$ 506,504	$ 521,812	$ 498,376	$ 2,029,183	$ 2,036,386	$ 2,002,850
Operating Income	36,089	32,583	42,361	28,693	43,124	41,805	51,113	35,402	139,726	171,444	173,674
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues									1,657,854	1,699,349	1,694,965
Operating Income									119,597	153,142	157,604
Value Added Services
Segment Reporting Information [Line Items]
Revenues									361,384	324,155	292,813
Operating Income									14,664	15,999	17,036
Other
Segment Reporting Information [Line Items]
Revenues									11,342	11,782	12,367
Operating Income									3,947	1,212	(383)
Corporate
Segment Reporting Information [Line Items]
Revenues									3,081	4,322	4,409
Operating Income									1,518	1,091	(583)
Subtotal [Member]
Segment Reporting Information [Line Items]
Revenues									2,033,661	2,039,608	2,004,554
Inter-segment eliminations
Segment Reporting Information [Line Items]
Revenues									$ (4,478)	$ (3,222)	$ (1,704)