Segment Reporting (Operating Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Segment Reporting Information [Line Items]
Revenues before Inter-segment Eliminations	$ 1,366,161	$ 1,245,627
Inter-segment Revenue Eliminations	55,646	49,301
Revenues from External Customers	1,366,161	1,245,627
Operating Income (Loss)	55,690	36,696
Freight [Member]
Segment Reporting Information [Line Items]
Revenues before Inter-segment Eliminations	831,047	767,741
Inter-segment Revenue Eliminations	12,406	11,291
Revenues from External Customers	818,641	756,450
Operating Income (Loss)	34,502	20,344
Logistics [Member]
Segment Reporting Information [Line Items]
Revenues before Inter-segment Eliminations	419,146	369,975
Inter-segment Revenue Eliminations	10,345	6,161
Revenues from External Customers	408,801	363,814
Operating Income (Loss)	12,294	8,646
Truckload [Member]
Segment Reporting Information [Line Items]
Revenues before Inter-segment Eliminations	157,323	145,215
Inter-segment Revenue Eliminations	19,566	20,846
Revenues from External Customers	137,757	124,369
Operating Income (Loss)	10,550	7,083
Other [Member]
Segment Reporting Information [Line Items]
Revenues before Inter-segment Eliminations	14,291	11,997
Inter-segment Revenue Eliminations	13,329	11,003
Revenues from External Customers	962	994
Operating Income (Loss)	(1,656)	623
Inter-Segment Revenue Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues before Inter-segment Eliminations	$ (55,646)	$ (49,301)

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

No definition available.

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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

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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.

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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.

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- Details

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