Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES:
Net income	$ 76,516	$ 17,827	$ 7,900
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	55,012	56,168	55,107
Bad debt expense	1,044	530	728
Stock compensation—net of excess tax benefits	441	460	912
Provision for deferred income taxes	17,832	5,362	1,625
Recognized (gain) loss on marketable equity securities	(8,197)	3,463	(4,753)
(Gain) loss on sale or disposal of equipment	(1,446)	373	583
Changes in operating assets and liabilities:
Accounts receivable	(47,132)	(17,835)	884
Prepaid expenses, deposits, inventories, and other assets	(865)	(1,780)	1,865
Income taxes refundable	591	(60)	1,372
Income taxes payable	4,364	0	0
Trade accounts payable	5,945	20,880	(2,233)
Accrued expenses and other liabilities	(2,365)	(17,798)	20,307
Net cash provided by operating activities	101,740	67,590	84,297
INVESTING ACTIVITIES:
Purchases of property and equipment	(19,144)	(48,226)	(79,354)
Proceeds from disposition of equipment	31,680	17,418	14,263
Sales of marketable equity securities	3,109	2,039	2,984
Purchases of marketable equity securities, net of return of capital	(6,395)	(3,923)	(203)
Net cash provided by (used in) investing activities	9,250	(32,692)	(62,310)
FINANCING ACTIVITIES:
Borrowings under line of credit	654,212	517,668	590,902
Repayments under line of credit	(672,458)	(516,468)	(584,047)
Borrowings of long-term debt	21,408	26,837	60,203
Repayments of long-term debt	(75,115)	(64,411)	(70,917)
Borrowings under margin account	6,510	7,068	527
Repayments under margin account	(16,547)	(3,292)	(4,334)
Repurchases of treasury stock	(10,828)	(2,281)	(14,285)
Net cash used in financing activities	(92,818)	(34,879)	(21,951)
NET INCREASE IN CASH AND CASH EQUIVALENTS	18,172	19	36
CASH AND CASH EQUIVALENTS—Beginning of year	337	318	282
CASH AND CASH EQUIVALENTS—End of year	18,509	337	318
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION—
Interest	8,144	8,798	8,612
Income taxes	3,870	281	671
NON-CASH INVESTING AND FINANCING ACTIVITIES—
Purchases of revenue equipment included in accounts payable	$ 383	$ 9,050	$ 366