Significant Accounting Policies - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from operations	$ 1,058,166	$ 1,048,457	$ 2,941,740	$ 3,099,905
LTL Service Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from operations	1,044,640	1,035,093	2,903,140	3,058,864
Other Service Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from operations	$ 13,526	$ 13,364	$ 38,600	$ 41,041