Segment Reporting (Operating Income(Loss)) (Details) (USD $) In Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segment Reporting Information [Line Items]
Revenues	$ 1,377,079	$ 1,270,183	$ 3,971,255	$ 3,738,357
Inter-segment Revenue Eliminations	54,228	48,015	156,569	174,695
Revenue from External Customers	1,377,079	1,270,183	3,971,255	3,738,357
Operating Income (Loss)	61,125	12,501	157,986	62,333
Other [Member]
Segment Reporting Information [Line Items]
Revenues	12,160	10,416	36,454	36,274
Inter-segment Revenue Eliminations	10,691	8,973	32,131	31,955
Revenue from External Customers	1,469	1,443	4,323	4,319
Operating Income (Loss)	(142)	246	(927)	2,034
Inter-Segment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(54,228)	(48,015)	(156,569)	(174,695)
Freight [Member]
Segment Reporting Information [Line Items]
Revenues	843,300	797,078	2,450,870	2,339,046
Inter-segment Revenue Eliminations	13,205	12,741	36,931	38,123
Revenue from External Customers	830,095	784,337	2,413,939	2,300,923
Operating Income (Loss)	40,721	13,062	100,220	27,135
Logistics [Member]
Segment Reporting Information [Line Items]
Revenues	417,142	370,049	1,181,129	1,111,007
Inter-segment Revenue Eliminations	9,411	5,447	24,216	13,977
Revenue from External Customers	407,731	364,602	1,156,913	1,097,030
Operating Income (Loss)	12,679	(6,282)	33,420	19,582
Truckload [Member]
Segment Reporting Information [Line Items]
Revenues	158,705	140,655	459,371	426,725
Inter-segment Revenue Eliminations	20,921	20,854	63,291	90,640
Revenue from External Customers	137,784	119,801	396,080	336,085
Operating Income (Loss)	$ 7,867	$ 5,475	$ 25,273	$ 13,582

The net result for the period of deducting operating expenses from operating revenues.

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- Definition

Aggregate revenue recognized during the period (derived from goods sold, services rendered, insurance premiums, or other activities that constitute an entity's earning process). For financial services companies, also includes investment and interest income, and sales and trading gains.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 5

-Section 03

-Paragraph 1

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

+ Details

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- Definition

Amount of revenue from external customers for the reportable segment. Such disclosure is presented if the amount is: (a) included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 131

-Paragraph 27

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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- Definition

Amount of revenue from transactions with other operating segments of the same entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 131

-Paragraph 27

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

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