Consolidated condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Cash flows provided by operating activities:
Net income	$ 44,376	$ 59,194
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	58,957	53,008
Tires in service amortization	3,584	3,161
Gain on disposition of revenue equipment	(8,796)	(9,352)
Deferred income taxes	(4,304)	4,809
Share-based payment arrangement compensation expense	1,359	1,573
Changes in other current operating items:
Receivables	13,087	(37,619)
Prepaid expenses and other	(3,633)	(5,040)
Accounts payable	(1,450)	19,927
Insurance and claims accruals	1,918	3,675
Accrued and other current liabilities	(6,897)	5,334
Net cash provided by operating activities	98,201	98,670
Cash flows used for investing activities:
Other	(45)	(38)
Net cash used for investing activities	(88,639)	(35,004)
Cash flows used for financing activities:
Dividends on common stock	(9,752)	(9,843)
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	1,044	919
Employee taxes paid in exchange for shares withheld	(926)	(1,610)
Net cash used for financing activities	(9,634)	(52,287)
Net change in cash and cash equivalents	(72)	11,379
Cash and cash equivalents:
Beginning of period	80,600	56,995
End of period	80,528	68,374
Supplemental non-cash disclosure:
Change in property and equipment not yet paid	5,870	9,765
Supplemental disclosure of cash flow information:
Cash paid for income taxes	6,809	9,045
Revenue Equipment [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of revenue equipment	(8,796)	(9,352)
Cash flows used for investing activities:
Revenue equipment	(118,294)	(54,202)
Proceeds from revenue equipment dispositions	34,000	23,854
Buildings And Land Office Equipment And Other [Member]
Cash flows used for investing activities:
Revenue equipment	(4,311)	(4,618)
Proceeds from revenue equipment dispositions	$ 11	$ 0