Consolidated condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Cash flows provided by operating activities:
Net income	$ 9,646	$ 22,502	$ 47,871
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	28,527	29,530
Tires in service amortization	1,763	1,765
Gain on disposition of revenue equipment	(1,171)	(5,246)
Deferred income taxes	(3,516)	784
Share-based payment arrangement compensation expense	353	354
Changes in other current operating items:
Receivables	6,025	9,135
Prepaid expenses and other	1,810	2,232
Accounts payable	2,197	(6,691)
Insurance and claims accruals	(2,720)	3,220
Accrued and other current liabilities	2,808	(8,353)
Net cash provided by operating activities	45,722	49,232
Cash flows used for investing activities:
Other	(49)	(45)
Net cash used for investing activities	(20,249)	(28,280)
Cash flows used for financing activities:
Dividends on common stock	(4,881)	(4,874)
Issuance of common stock from share-based payment arrangement exercises, deferred compensation plan distributions and vesting of performance unit awards	307	536
Employee taxes paid in exchange for shares withheld	(382)	(926)
Net cash used for financing activities	(4,956)	(5,264)
Net change in cash and cash equivalents	20,517	15,688
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations	73,730	96,288	$ 53,213	$ 80,600
Supplemental non-cash disclosure:
Change in property and equipment not yet paid	(6,780)	2,561
Cash paid for income taxes	0	22
Revenue Equipment [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of revenue equipment	(1,171)	(5,246)
Cash flows used for investing activities:
Revenue equipment	(28,443)	(42,358)
Proceeds from revenue equipment dispositions	10,075	16,218
Buildings And Land Office Equipment And Other [Member]
Cash flows used for investing activities:
Revenue equipment	(1,840)	(2,106)
Proceeds from revenue equipment dispositions	$ 8	$ 11