Condensed Consolidated Statements of Earnings (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Operating revenues, excluding fuel surcharge revenues	$ 3,132,623	$ 3,837,532	$ 6,362,212	$ 7,326,120
Operating expenses:
Rents and purchased transportation	1,404,586	1,920,823	2,872,384	3,758,163
Salaries, wages and employee benefits	821,876	841,825	1,646,875	1,605,416
Fuel and fuel taxes	171,846	265,636	367,680	455,102
Depreciation and amortization	179,972	157,571	355,784	306,334
Operating supplies and expenses	128,949	126,383	257,308	233,322
Insurance and claims	63,893	87,258	134,221	133,389
General and administrative expenses, net of asset dispositions	61,472	59,764	121,879	97,209
Operating taxes and licenses	18,951	16,323	37,058	32,073
Communication and utilities	10,366	8,866	20,822	17,735
Total operating expenses	2,861,911	3,484,449	5,814,011	6,638,743
Operating income	270,712	353,083	548,201	687,377
Net interest expense	14,604	12,842	29,393	25,429
Earnings before income taxes	256,108	340,241	518,808	661,948
Income taxes	66,556	84,899	131,488	163,282
Net earnings	$ 189,552	$ 255,342	$ 387,320	$ 498,666
Weighted average basic shares outstanding (in shares)	103,562	104,252	103,643	104,572
Basic earnings per share (in dollars per share)	$ 1.83	$ 2.45	$ 3.74	$ 4.77
Weighted average diluted shares outstanding (in shares)	104,566	105,387	104,647	105,729
Diluted earnings per share (in dollars per share)	$ 1.81	$ 2.42	$ 3.70	$ 4.72
Service Excluding Fuel Surcharge [Member]
Operating revenues, excluding fuel surcharge revenues	$ 2,707,560	$ 3,159,759	$ 5,450,070	$ 6,201,976
Fuel Surcharge [Member]
Operating revenues, excluding fuel surcharge revenues	$ 425,063	$ 677,773	$ 912,142	$ 1,124,144