Condensed Consolidated Statements of Earnings (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Operating revenues	$ 3,837,532	$ 2,908,370	$ 7,326,120	$ 5,526,519
Operating expenses:
Rents and purchased transportation	1,920,823	1,538,232	3,758,163	2,890,533
Salaries, wages and employee benefits	841,825	665,471	1,605,416	1,285,502
Fuel and fuel taxes	265,636	126,841	455,102	239,881
Depreciation and amortization	157,571	139,371	306,334	276,916
Operating supplies and expenses	126,383	91,019	233,322	172,717
Insurance and claims	87,258	35,508	133,389	73,538
General and administrative expenses, net of asset dispositions	59,764	47,505	97,209	92,396
Operating taxes and licenses	16,323	14,209	32,073	28,024
Communication and utilities	8,866	8,668	17,735	17,814
Total operating expenses	3,484,449	2,666,824	6,638,743	5,077,321
Operating income	353,083	241,546	687,377	449,198
Net interest expense	12,842	12,059	25,429	24,084
Earnings before income taxes	340,241	229,487	661,948	425,114
Income taxes	84,899	57,325	163,282	106,346
Net earnings	$ 255,342	$ 172,162	$ 498,666	$ 318,768
Weighted average basic shares outstanding (in shares)	104,252	105,509	104,572	105,594
Basic earnings per share (in dollars per share)	$ 2.45	$ 1.63	$ 4.77	$ 3.02
Weighted average diluted shares outstanding (in shares)	105,387	106,816	105,729	106,816
Diluted earnings per share (in dollars per share)	$ 2.42	$ 1.61	$ 4.72	$ 2.98
Service Excluding Fuel Surcharge [Member]
Operating revenues	$ 3,159,759	$ 2,606,981	$ 6,201,976	$ 4,995,015
Fuel Surcharge [Member]
Operating revenues	$ 677,773	$ 301,389	$ 1,124,144	$ 531,504