Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net earnings	$ 243,325	$ 146,606
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	148,763	137,545
Noncash lease expense	18,461	12,296
Share-based compensation	19,141	14,967
(Gain)/loss on sale of revenue equipment and other	(17,262)	1,147
Deferred income taxes	8,285	30,996
Changes in operating assets and liabilities:
Trade accounts receivable	(232,920)	(94,759)
Other assets	35,734	46,385
Trade accounts payable	86,959	43,280
Income taxes payable or receivable	33,688	12,156
Claims accruals	13,357	2,242
Accrued payroll and other accrued expenses	(65,746)	11,797
Net cash provided by operating activities	291,785	364,658
Cash flows from investing activities:
Additions to property and equipment	(309,338)	(108,775)
Net proceeds from sale of equipment	20,212	22,921
Business acquisition	(86,939)	0
Changes in other assets	0	4
Net cash used in investing activities	(376,065)	(85,850)
Cash flows from financing activities:
Proceeds from revolving lines of credit and other	0	505
Purchase of treasury stock	(75,018)	(5,239)
Stock repurchased for payroll taxes and other	(9,782)	(4,809)
Dividends paid	(41,940)	(29,597)
Net cash used in financing activities	(126,740)	(39,140)
Net change in cash and cash equivalents	(211,020)	239,668
Cash and cash equivalents at beginning of period	355,549	313,302
Cash and cash equivalents at end of period	144,529	552,970
Supplemental disclosure of cash flow information:
Interest	20,974	21,343
Income taxes	22,153	3,779
Noncash investing activities
Accruals for equipment received	$ 52,195	$ 23,630