Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
OPERATING ACTIVITIES:
Net income	$ 18,416	$ 90,672	$ 76,516
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	64,605	62,806	55,012
Bad debt expense	2,396	917	1,044
Stock compensation—net of excess tax benefits	553	715	441
Provision for deferred income taxes	2,886	14,541	17,832
Recognized (gain) on marketable equity securities	(1,618)	(1,129)	(8,197)
Gain on disposition of equipment	(1,043)	(3,250)	(1,446)
Changes in operating assets and liabilities:
Accounts receivable	50,798	(2,152)	(47,132)
Prepaid expenses, deposits, inventories, and other assets	2,538	(7,257)	(865)
Income taxes refundable	1,768	(5,373)	591
Income taxes payable	0	(4,364)	4,364
Trade accounts payable	(10,980)	2,198	5,945
Accrued expenses and other liabilities	(15,742)	20,491	(2,365)
Net cash provided by operating activities	114,577	168,815	101,740
INVESTING ACTIVITIES:
Purchases of property and equipment	(34,060)	(63,961)	(19,144)
Purchase of a business, net of cash acquired	0	(65,797)	0
Proceeds from disposition of equipment	22,622	17,406	31,680
Sales of marketable equity securities	143	0	3,109
Purchases of marketable equity securities, net of return of capital	0	(1,175)	(6,395)
Net cash (used in) provided by investing activities	(11,295)	(113,527)	9,250
FINANCING ACTIVITIES:
Borrowings under line of credit	879,191	945,610	654,212
Repayments under line of credit	(879,191)	(945,610)	(672,458)
Borrowings of long-term debt	0	74,925	21,408
Repayments of long-term debt	(71,105)	(67,335)	(75,115)
Borrowings under margin account	46	1,229	6,510
Repayments under margin account	(960)	(1,529)	(16,547)
Repurchases of treasury stock	(4,736)	(7,000)	(10,828)
Net cash (used in) provided by financing activities	(76,755)	290	(92,818)
NET INCREASE IN CASH AND CASH EQUIVALENTS	26,527	55,578	18,172
CASH AND CASH EQUIVALENTS—Beginning of year	74,087	18,509	337
CASH AND CASH EQUIVALENTS—End of year	100,614	74,087	18,509
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION—
Interest	9,762	7,842	8,144
Income taxes	5,510	23,243	3,870
NON-CASH INVESTING AND FINANCING ACTIVITIES—
Purchases of revenue equipment included in accounts payable	$ 25,147	$ 431	$ 383