Consolidated condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows provided by operating activities:
Net income	$ 57,974	$ 84,840
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	87,974	81,389
Tires in service amortization	5,415	4,861
Gain on disposition of revenue equipment	(11,810)	(10,422)
Deferred income taxes	(11,154)	5,431
Share-based payment arrangement compensation expense	1,860	2,228
Changes in other current operating items:
Receivables	5,487	(24,657)
Prepaid expenses and other	(2,402)	(3,901)
Accounts payable	1,239	14,364
Insurance and claims accruals	535	3,650
Accrued and other current liabilities	(8,785)	5,438
Net cash provided by operating activities	126,333	163,221
Cash flows used for investing activities:
Other	(45)	(38)
Net cash used for investing activities	(124,470)	(92,416)
Cash flows used for financing activities:
Dividends on common stock	(14,630)	(14,709)
Repurchase and retirement of common stock	0	(41,753)
Issuance of common stock from share-based payment arrangement exercises, deferred compensation plan distributions and vesting of performance unit awards	1,160	1,764
Employee taxes paid in exchange for shares withheld	(926)	(1,610)
Net cash used for financing activities	(14,396)	(56,308)
Net change in cash and cash equivalents	(12,533)	14,497
Cash and cash equivalents:
Beginning of period	80,600	56,995
End of period	68,067	71,492
Supplemental non-cash disclosure:
Change in property and equipment not yet paid	(2,542)	10,132
Operating lease assets and liabilities acquired	89	0
Cash paid for income taxes	19,360	16,413
Interest	10	52
Revenue Equipment [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of revenue equipment	(11,810)	(10,422)
Cash flows used for investing activities:
Revenue equipment	(167,985)	(110,535)
Proceeds from revenue equipment dispositions	51,125	28,527
Buildings And Land Office Equipment And Other [Member]
Cash flows used for investing activities:
Revenue equipment	(7,586)	(10,370)
Proceeds from revenue equipment dispositions	$ 21	$ 0