Segment Reporting (Operating Income (Loss)) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting [Abstract]
Number of Reportable Segments			3
Change in Allocation of Pension Costs to Segments	$ 700,000	$ 2,400,000	$ 2,200,000	$ 7,200,000
Segment Reporting Information [Line Items]
Revenues	1,398,021,000	1,404,113,000	4,115,555,000	4,216,370,000
Operating Income (Loss)	67,675,000	55,213,000	175,573,000	191,046,000
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	2,100,000	1,076,000	5,579,000	3,154,000
Operating Segments [Member] | Freight [Member]
Segment Reporting Information [Line Items]
Revenues	888,508,000	846,280,000	2,587,468,000	2,529,979,000
Operating Income (Loss)	51,570,000	34,441,000	122,283,000	122,372,000
Operating Segments [Member] | Logistics [Member]
Segment Reporting Information [Line Items]
Revenues	362,830,000	415,165,000	1,095,086,000	1,260,173,000
Operating Income (Loss)	8,178,000	10,990,000	20,749,000	35,972,000
Operating Segments [Member] | Truckload [Member]
Segment Reporting Information [Line Items]
Revenues	144,583,000	141,592,000	427,422,000	423,064,000
Operating Income (Loss)	8,971,000	11,273,000	29,799,000	36,442,000
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	64,471,000	57,276,000	182,814,000	170,935,000
Intersegment Eliminations [Member] | Freight [Member]
Segment Reporting Information [Line Items]
Revenues	10,746,000	11,996,000	31,597,000	37,868,000
Intersegment Eliminations [Member] | Logistics [Member]
Segment Reporting Information [Line Items]
Revenues	17,719,000	12,625,000	48,198,000	34,792,000
Intersegment Eliminations [Member] | Truckload [Member]
Segment Reporting Information [Line Items]
Revenues	17,596,000	18,502,000	53,564,000	57,273,000
Corporate and Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	18,410,000	14,153,000	49,455,000	41,002,000
Operating Income (Loss)	$ (1,044,000)	$ (1,491,000)	$ 2,742,000	$ (3,740,000)