Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
OPERATING ACTIVITIES
Net income	$ 133,584	$ 79,277	$ 70,806
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	133,047	104,232	110,381
Deferred income taxes	2,412	(5,869)	8,148
Stock-based compensation expense	1,399	1,150	2,092
Debt-related amortization	360	0	0
Gain on disposal of property and equipment	(96,906)	(37,438)	(14,830)
Changes in certain working capital items (net of acquisition):
Trade receivables	20,033	2,765	1,176
Prepaid expenses and other current assets	845	3,657	(3,628)
Accounts payable, accrued liabilities, and accrued expenses	(1,227)	(18,476)	3,062
Accrued income taxes	1,166	(5,880)	1,643
Net cash provided by operating activities	194,713	123,418	178,850
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	172,750	130,184	93,160
Purchases of property and equipment, net of trades	(160,568)	(132,640)	(204,337)
Acquisition of business, net of cash acquired	(675,852)	0	0
Change in other assets	411	(191)	129
Net cash used in investing activities	(663,259)	(2,647)	(111,048)
FINANCING ACTIVITIES
Cash dividends paid	(6,318)	(45,872)	(6,502)
Proceeds from issuance of long-term debt	447,343	0	0
Shares withheld for employee taxes related to stock-based compensation	(290)	(247)	(582)
Repayments on finance leases and debt	(81,478)	0	0
Repurchases of common stock	0	(32,025)	(25,654)
Net cash provided by (used in) financing activities	359,257	(78,144)	(32,738)
Net increase (decrease) in cash and cash equivalents	(109,289)	42,627	35,064
CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Beginning of period	173,767	131,140	96,076
End of period	64,478	173,767	131,140
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid during the period for interest expense	6,384	0	0
Cash paid during the period for income taxes, net of refunds	44,010	38,519	13,664
Noncash investing and financing activities:
Fair value of revenue equipment traded	428	0	0
Purchased property and equipment in accounts payable	11,938	9,019	2,172
Sold revenue equipment and property in other current assets	1,558	1,512	3,383
Treasury stock acquired in accounts payable	0	0	485
Right-of-use assets obtained in exchange for operating lease liabilities	3,345	0	0
RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Cash and cash equivalents	49,462	157,742	113,852
Restricted cash included in other current assets	752	928	1,075
Restricted cash included in other assets	14,264	15,097	16,213
Total cash, cash equivalents and restricted cash	$ 64,478	$ 173,767	$ 131,140