(Goodwill acquired in business combination by reportable segment) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2014
Rollforward of goodwill by reportable segment
Goodwill balance as of December 31, 2013	$ 518,743
Goodwill, Purchase Accounting Adjustments	(206)
Goodwill related to acquisitions	149,592
Goodwill balance as of September 30, 2014	668,129
LTL [Member]
Rollforward of goodwill by reportable segment
Goodwill, Purchase Accounting Adjustments	0
Goodwill related to acquisitions	0
Goodwill balance as of September 30, 2014	197,312
TL [Member]
Rollforward of goodwill by reportable segment
Goodwill balance as of December 31, 2013	211,413
Goodwill, Purchase Accounting Adjustments	0
Goodwill related to acquisitions	110,656
Goodwill balance as of September 30, 2014	322,069
TMS [Member]
Rollforward of goodwill by reportable segment
Goodwill balance as of December 31, 2013	110,018
Goodwill, Purchase Accounting Adjustments	(206)
Goodwill related to acquisitions	38,936
Goodwill balance as of September 30, 2014	$ 148,748

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

+ Details

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

+ Details

Name:	us-gaap_GoodwillAcquiredDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 25

-Paragraph 16

-URI http://asc.fasb.org/extlink&oid=21917927&loc=d3e961-128460

+ Details

Name:	us-gaap_GoodwillPurchaseAccountingAdjustments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_GoodwillRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration