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, 2018
Dec. 31, 2017
Dec. 31, 2016
Jun. 30, 2018
Goodwill [Line Items]        
Business Acquisition, Goodwill, Expected Tax Deductible Amount $ 119,948      
Goodwill, Net 199,092 $ 191,671    
Amortization expense of acquired intangible assets $ 9,138 10,193 $ 10,122  
Customer Relationships [Member]        
Goodwill [Line Items]        
Finite-Lived Intangible Asset, Useful Life 15 years 11 days      
Noncompete Agreements [Member]        
Goodwill [Line Items]        
Finite-Lived Intangible Asset, Useful Life 4 years 6 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      
TQI [Member]        
Goodwill [Line Items]        
Discount rate       16.50%
Percentage of Fair Value in Excess of Carrying Amount 36.00%      
Long-term growth rate       4.00%
Expedited LTL [Member]        
Goodwill [Line Items]        
Discount rate       12.00%
Percentage of Fair Value in Excess of Carrying Amount 349.00%      
Goodwill, Net $ 97,593 97,593    
Long-term growth rate       4.00%
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]        
Discount rate       15.50%
Percentage of Fair Value in Excess of Carrying Amount 182.00%      
Goodwill, Net $ 12,359 12,359    
Accumulated impairment loss $ (6,953) (6,953)    
Long-term growth rate       4.00%
Intermodal [Member]        
Goodwill [Line Items]        
Discount rate       14.00%
Percentage of Fair Value in Excess of Carrying Amount 73.00%      
Goodwill, Net $ 76,615 $ 69,194    
Long-term growth rate       4.00%
MMT [Member]        
Goodwill [Line Items]        
Goodwill, Net 1,954      
Goodwill, Acquired During Period $ 1,954      
MMT [Member] | Customer Relationships [Member]        
Goodwill [Line Items]        
Weighted average useful lives of acquired intangible assets 15 years      
MMT [Member] | Noncompete Agreements [Member]        
Goodwill [Line Items]        
Weighted average useful lives of acquired intangible assets 4 years      
Southwest Freight Distributors [Member]        
Goodwill [Line Items]        
Goodwill, Net $ 5,467      
Goodwill, Acquired During Period $ 5,467      
Southwest Freight Distributors [Member] | Customer Relationships [Member]        
Goodwill [Line Items]        
Weighted average useful lives of acquired intangible assets 10 years      
Southwest Freight Distributors [Member] | Noncompete Agreements [Member]        
Goodwill [Line Items]        
Weighted average useful lives of acquired intangible assets 3 years      
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