Significant Accounting Policies - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from operations	$ 1,319,409	$ 896,210	$ 2,445,924	$ 1,883,574
LTL Service Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from operations	1,299,760	884,069	2,409,382	1,858,500
Other Service Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from operations	$ 19,649	$ 12,141	$ 36,542	$ 25,074