Summary of Operating Results (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Revenue	$ 835,941us-gaap_SalesRevenueServicesNet	$ 848,449us-gaap_SalesRevenueServicesNet
Transportation costs	746,813us-gaap_CostOfServices	759,705us-gaap_CostOfServices
Gross margin	89,128us-gaap_GrossProfit	88,744us-gaap_GrossProfit
Costs and expenses:
Salaries and benefits	39,476us-gaap_LaborAndRelatedExpense	37,092us-gaap_LaborAndRelatedExpense
Agent fees and commissions	14,826us-gaap_SalesCommissionsAndFees	13,666us-gaap_SalesCommissionsAndFees
General and administrative	14,071us-gaap_GeneralAndAdministrativeExpense	15,432us-gaap_GeneralAndAdministrativeExpense
Depreciation and amortization	1,960us-gaap_DepreciationAndAmortization	2,058us-gaap_DepreciationAndAmortization
Total costs and expenses	70,333us-gaap_OperatingExpenses	68,248us-gaap_OperatingExpenses
Operating income	18,795us-gaap_OperatingIncomeLoss	20,496us-gaap_OperatingIncomeLoss
Capital Expenditures	15,057	33,035
Operating Segments [Member] \| Hub [Member]
Segment Reporting Information [Line Items]
Revenue	643,443	653,409
Transportation costs	580,258	588,912
Gross margin	63,185	64,497
Costs and expenses:
Salaries and benefits	35,660	33,337
Agent fees and commissions	15	11
General and administrative	12,198	13,739
Depreciation and amortization	1,618	1,517
Total costs and expenses	49,491	48,604
Operating income	13,694	15,893
Capital Expenditures	14,998	32,880
Operating Segments [Member] \| Mode [Member]
Segment Reporting Information [Line Items]
Revenue	213,522	208,906
Transportation costs	187,579	184,659
Gross margin	25,943	24,247
Costs and expenses:
Salaries and benefits	3,816	3,755
Agent fees and commissions	14,811	13,655
General and administrative	1,873	1,693
Depreciation and amortization	342	541
Total costs and expenses	20,842	19,644
Operating income	5,101	4,603
Capital Expenditures	59	155
Intersegment Elims [Member]
Segment Reporting Information [Line Items]
Revenue	(21,024)	(13,866)
Transportation costs	$ (21,024)	$ (13,866)

Total costs related to services rendered by an entity during the reporting period.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 2

-Article 5

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 210.5-03.2(d))

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+ References

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

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-Name Accounting Standards Codification

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-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (a)

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

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

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

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

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-Subparagraph (SX 210.5-03.1(d))

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