Segment Reporting (Operating Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Revenues from External Customers	$ 1,381,370	$ 1,446,096	$ 2,717,534	$ 2,812,257
Revenues from Internal Customers	61,008	58,013	118,343	113,659
Operating Income (Loss)	76,299	80,143	107,898	135,833
Freight [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers	881,824	865,058	1,698,960	1,683,699
Revenues from Internal Customers	10,451	13,466	20,851	25,872
Operating Income (Loss)	54,689	53,429	70,713	87,931
Logistics [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers	353,528	436,207	732,256	845,008
Revenues from Internal Customers	16,850	11,822	30,479	22,167
Operating Income (Loss)	6,039	12,688	12,571	24,982
Truckload [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers	144,490	143,715	282,839	281,472
Revenues from Internal Customers	17,314	19,205	35,968	38,771
Operating Income (Loss)	10,873	14,619	20,828	25,169
Corporate and Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from External Customers	1,528	1,116	3,479	2,078
Revenues from Internal Customers	16,393	13,520	31,045	26,849
Operating Income (Loss)	$ 4,698	$ (593)	$ 3,786	$ (2,249)