Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net earnings	$ 352,028	$ 371,644
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	392,786	370,728
Noncash lease expense	34,110	28,731
Share-based compensation	48,658	42,154
Loss on sale of revenue equipment and other	2,255	9,085
Deferred income taxes	12,223	644
Changes in operating assets and liabilities:
Trade accounts receivable	(109,996)	9,579
Other assets	7,910	16,356
Trade accounts payable	86,867	64,578
Income taxes payable or receivable	45,411	89,975
Claims accruals	(5,440)	(4,749)
Accrued payroll and other accrued expenses	44,182	(61,130)
Net cash provided by operating activities	910,994	937,595
Cash flows from investing activities:
Additions to property and equipment	(559,763)	(722,371)
Net proceeds from sale of equipment	111,042	135,764
Business acquisition	0	(98,232)
Changes in other assets	49	(77)
Net cash used in investing activities	(448,672)	(684,916)
Cash flows from financing activities:
Proceeds from issuances of long-term debt	0	700,000
Payments on long-term debt	0	(250,000)
Proceeds from revolving lines of credit and other	221,618	1,590,506
Payments on revolving lines of credit and other	(220,100)	(1,904,000)
Purchase of treasury stock	(75,193)	(225,680)
Stock repurchased for payroll taxes and other	(19,390)	(11,886)
Dividends paid	(85,708)	(84,087)
Net cash used in financing activities	(178,773)	(185,147)
Net change in cash and cash equivalents	283,549	67,532
Cash and cash equivalents at beginning of period	35,000	7,600
Cash and cash equivalents at end of period	318,549	75,132
Supplemental disclosure of cash flow information:
Interest	47,095	42,111
Income taxes	58,497	33,738
Noncash investing activities
Accruals for equipment received	$ 36,010	$ 26,934