Annual report pursuant to Section 13 and 15(d)

Operating Leases (Details)

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Operating Leases (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Operating Leased Assets [Line Items]      
Operating lease renewal option, minimum (in years) 1 year    
Operating lease renewal option, maximum (in years) 10 years    
Operating lease original term, for tractors, trucks and trailers, minimum (in years) 3 years    
Operating lease original term, for tractors, trucks and trailers, maximum (in years) 5 years    
Sublease rental income $ 1,724 $ 1,923 $ 1,517
Expected future sublease rental income 1,155    
Operating Leases, Future Minimum Payments Due [Abstract]      
2019 51,380    
2020 40,999    
2021 29,598    
2022 16,612    
2023 9,234    
Thereafter 11,459    
Total $ 159,282