Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies Significant Accounting Policies (Disaggregated Revenue) (Details)

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Significant Accounting Policies Significant Accounting Policies (Disaggregated Revenue) (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Disaggregated Revenue [Line Items]        
Revenue from operations $ 872,987,000 $ 782,611,000 $ 2,466,995,000 $ 2,245,779,000
LTL Service Revenue [Member]        
Disaggregated Revenue [Line Items]        
Revenue from operations 859,832,000 769,854,000 2,426,419,000 2,206,642,000
Other Service Revenue [Member]        
Disaggregated Revenue [Line Items]        
Revenue from operations $ 13,155,000 $ 12,757,000 $ 40,576,000 $ 39,137,000