CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
CURRENT ASSETS
Cash and cash equivalents	$ 262,226	$ 158,264
Short-term investments	67,842	167,662
Accounts receivable, less allowances (2023 - $10,346; 2022 - $13,892)	430,122	517,494
Other accounts receivable, less allowances (2023 - $731; 2022 - $713)	52,124	11,016
Prepaid expenses	37,034	39,484
Prepaid and refundable income taxes	24,319	19,239
Current assets of discontinued operations		64,736
Other	11,116	11,888
TOTAL CURRENT ASSETS	884,783	989,783
PROPERTY, PLANT AND EQUIPMENT
Land and structures	460,068	401,840
Revenue equipment	1,126,055	1,038,832
Service, office, and other equipment	319,466	298,234
Software	173,354	167,164
Leasehold improvements	24,429	23,466
TOTAL PROPERTY, PLANT AND EQUIPMENT, Gross	2,103,372	1,929,536
Less allowances for depreciation and amortization	1,188,548	1,129,366
PROPERTY, PLANT AND EQUIPMENT, net	914,824	800,170
GOODWILL	304,753	304,753
INTANGIBLE ASSETS, net	101,150	113,733
OPERATING RIGHT-OF-USE ASSETS	169,999	166,515
DEFERRED INCOME TAXES	8,140	6,342
LONG-TERM ASSETS OF DISCONTINUED OPERATIONS		11,097
OTHER LONG-TERM ASSETS	101,445	101,893
TOTAL ASSETS	2,485,094	2,494,286
CURRENT LIABILITIES
Accounts payable	214,004	269,854
Income taxes payable	10,410	16,017
Accrued expenses	378,029	338,457
Current portion of long-term debt	66,948	66,252
Current portion of operating lease liabilities	32,172	26,225
Current liabilities of discontinued operations		51,665
TOTAL CURRENT LIABILITIES	701,563	768,470
LONG-TERM DEBT, less current portion	161,990	198,371
OPERATING LEASE LIABILITIES, less current portion	176,621	147,828
POSTRETIREMENT LIABILITIES, less current portion	13,319	12,196
LONG-TERM LIABILITIES OF DISCONTINUED OPERATIONS		781
CONTINGENT CONSIDERATION	92,900	112,000
OTHER LONG-TERM LIABILITIES	40,553	42,745
DEFERRED INCOME TAXES	55,785	60,494
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value, authorized 70,000,000 shares; issued 2023: 30,024,125 shares; 2022: 29,758,716 shares	300	298
Additional paid-in capital	340,961	339,582
Retained earnings	1,272,584	1,088,693
Treasury stock, at cost, 2023: 6,460,137 shares; 2022: 5,529,383 shares	(375,806)	(284,275)
Accumulated other comprehensive income	4,324	7,103
TOTAL STOCKHOLDERS' EQUITY	1,242,363	1,151,401
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 2,485,094	$ 2,494,286