Annual report pursuant to Section 13 and 15(d)

Acquisitions, Goodwill and Other Long-Lived Assets Carrying Value of Goodwill (Details)

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Acquisitions, Goodwill and Other Long-Lived Assets Carrying Value of Goodwill (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Goodwill [Line Items]      
Business Acquisition, Goodwill, Expected Tax Deductible Amount $ 112,527    
Goodwill, Net 191,671 $ 184,675  
Goodwill, Acquired During Period 6,996    
Amortization expense of acquired intangible assets $ 10,193 10,122 $ 10,905
Customer Relationships [Member]      
Goodwill [Line Items]      
Finite-Lived Intangible Asset, Useful Life 15 years 10 months 11 days    
Noncompete Agreements [Member]      
Goodwill [Line Items]      
Finite-Lived Intangible Asset, Useful Life 5 years 2 months 11 days    
Trade Names [Member]      
Goodwill [Line Items]      
Finite-Lived Intangible Asset, Useful Life 4 years 11 days    
Atlantic [Member] | Customer Relationships [Member]      
Goodwill [Line Items]      
Weighted average useful lives of acquired intangible assets 15 years    
Atlantic [Member] | Noncompete Agreements [Member]      
Goodwill [Line Items]      
Weighted average useful lives of acquired intangible assets 5 years    
KCL [Member] | Customer Relationships [Member]      
Goodwill [Line Items]      
Weighted average useful lives of acquired intangible assets 15 years    
KCL [Member] | Noncompete Agreements [Member]      
Goodwill [Line Items]      
Weighted average useful lives of acquired intangible assets 2 years    
Expedited LTL [Member]      
Goodwill [Line Items]      
Goodwill, Net $ 97,593 97,593  
Truckload Premium Services [Member]      
Goodwill [Line Items]      
Goodwill, Net 45,164 45,164  
Accumulated impairment loss (25,686) (25,686)  
Pool Distribution [Member]      
Goodwill [Line Items]      
Goodwill, Net 12,359 12,359  
Accumulated impairment loss (6,953) (6,953)  
Intermodal [Member]      
Goodwill [Line Items]      
Goodwill, Net 69,194 $ 62,198  
Goodwill, Acquired During Period $ 6,996    
Triumph & Ace [Member] | Customer Relationships [Member]      
Goodwill [Line Items]      
Weighted average useful lives of acquired intangible assets 15 years    
Triumph & Ace [Member] | Noncompete Agreements [Member]      
Goodwill [Line Items]      
Weighted average useful lives of acquired intangible assets 5 years