Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net earnings	$ 760,806	$ 506,035	$ 516,320
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	557,093	527,375	499,145
Noncash lease expense	55,137	45,985	39,517
Share-based compensation	61,505	60,698	53,324
Loss on sale of revenue equipment and other	5,540	4,389	13,057
Deferred income taxes	53,420	(7,056)	55,617
Changes in operating assets and liabilities:
Trade accounts receivable	(382,216)	(109,758)	50,310
Income taxes receivable or payable	(30,633)	57,851	41,447
Other current assets	(15,252)	(18,038)	(4,975)
Trade accounts payable	140,295	(5,482)	(85,327)
Claims accruals	35,051	(9,072)	(20,727)
Accrued payroll and other accrued expenses	(16,848)	69,932	(59,361)
Net cash provided by operating activities	1,223,898	1,122,859	1,098,347
Cash flows from investing activities:
Additions to property and equipment	(947,563)	(738,545)	(854,115)
Proceeds from sale of equipment	70,545	137,776	165,918
Business acquisition	0	(12,136)	(115,654)
Change in other assets	0	(52)	(111)
Net cash used in investing activities	(877,018)	(612,957)	(803,962)
Cash flows from financing activities:
Proceeds from long-term debt	0	0	700,000
Payments on long-term debt	0	0	(250,000)
Proceeds from revolving lines of credit and other	0	222,124	1,591,014
Payments on revolving lines of credit and other	0	(220,100)	(1,904,000)
Purchase of treasury stock	(151,720)	(92,548)	(275,657)
Stock repurchased for payroll taxes and other	(28,471)	(26,842)	(16,525)
Dividends paid	(124,442)	(114,234)	(111,817)
Net cash used in financing activities	(304,633)	(231,600)	(266,985)
Net increase in cash and cash equivalents	42,247	278,302	27,400
Cash and cash equivalents at beginning of year	313,302	35,000	7,600
Cash and cash equivalents at end of year	355,549	313,302	35,000
Supplemental disclosure of cash flow information:
Interest	47,016	48,351	46,721
Income taxes	203,740	95,454	71,681
Noncash investing activities
Accruals for equipment received	$ 60,464	$ 12,533	$ 25,505