Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net earnings	$ 104,834	$ 119,601
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	130,095	119,930
Noncash lease expense	11,411	8,484
Share-based compensation	18,063	13,571
Loss on sale of revenue equipment and other	1,472	2,252
Deferred income taxes	15,470	25,030
Changes in operating assets and liabilities:
Trade accounts receivable	33,549	58,109
Other assets	(60,029)	(54,421)
Trade accounts payable	(5,392)	(14,325)
Income taxes payable or receivable	23,066	12,213
Claims accruals	(7,938)	(920)
Accrued payroll and other accrued expenses	(15,438)	(38,783)
Net cash provided by operating activities	249,163	250,741
Cash flows from investing activities:
Additions to property and equipment	(166,814)	(257,658)
Net proceeds from sale of equipment	38,078	45,512
Business acquisition	0	(98,543)
Change in other assets	28	(15)
Net cash used in investing activities	(128,708)	(310,704)
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	220,607	730,618
Payments on revolving lines of credit and other	(220,100)	(1,045,100)
Purchase of treasury stock	(75,193)	0
Stock repurchased for payroll taxes	(3,627)	(2,520)
Dividends paid	(28,688)	(28,272)
Net cash provided by/(used in) financing activities	(107,001)	104,726
Net change in cash and cash equivalents	13,454	44,763
Cash and cash equivalents at beginning of period	35,000	7,600
Cash and cash equivalents at end of period	48,454	52,363
Supplemental disclosure of cash flow information:
Interest	21,673	14,363
Income taxes	1,173	2,163
Noncash investing activities
Accruals for equipment received	$ 22,395	$ 49,639