Segment Information (Summary Of Segment Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 542,120	$ 506,648	$ 1,034,142	$ 999,535
Operating Income	42,330	42,361	65,771	71,054
Truckload Transportation Services
Segment Reporting Information [Line Items]
Revenues	429,390	412,869	832,575	821,769
Operating Income	38,320	34,442	59,100	58,057
Value Added Services
Segment Reporting Information [Line Items]
Revenues	100,501	91,185	185,655	173,695
Operating Income	2,255	4,489	4,110	8,102
Other Segment
Segment Reporting Information [Line Items]
Revenues	12,258	2,083	16,247	4,127
Operating Income	357	1,623	841	2,528
Corporate Segment
Segment Reporting Information [Line Items]
Revenues	829	996	1,387	1,646
Operating Income	1,398	1,807	1,720	2,367
Subtotal
Segment Reporting Information [Line Items]
Revenues	542,978	507,133	1,035,864	1,001,237
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	$ (858)	$ (485)	$ (1,722)	$ (1,702)