CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
CURRENT ASSETS
Cash and cash equivalents	$ 172,855	$ 262,226
Short-term investments	68,065	67,842
Accounts receivable, less allowances (2024 - $9,184; 2023 - $10,346)	433,717	430,122
Other accounts receivable, less allowances (2024 - $733; 2023 - $731)	11,389	52,124
Prepaid expenses	39,232	37,034
Prepaid and refundable income taxes	22,084	24,319
Other	11,136	11,116
TOTAL CURRENT ASSETS	758,478	884,783
PROPERTY, PLANT AND EQUIPMENT
Land and structures	491,555	460,068
Revenue equipment	1,119,446	1,126,055
Service, office, and other equipment	318,252	319,466
Software	176,988	173,354
Leasehold improvements	25,173	24,429
TOTAL PROPERTY, PLANT AND EQUIPMENT, Gross	2,131,414	2,103,372
Less allowances for depreciation and amortization	1,193,584	1,188,548
PROPERTY, PLANT AND EQUIPMENT, net	937,830	914,824
GOODWILL	304,753	304,753
INTANGIBLE ASSETS, net	97,940	101,150
OPERATING RIGHT-OF-USE ASSETS	174,987	169,999
DEFERRED INCOME TAXES	10,032	8,140
OTHER LONG-TERM ASSETS	73,123	101,445
TOTAL ASSETS	2,357,143	2,485,094
CURRENT LIABILITIES
Accounts payable	209,908	214,004
Income taxes payable	8	10,410
Accrued expenses	313,494	378,029
Current portion of long-term debt	63,179	66,948
Current portion of operating lease liabilities	31,986	32,172
TOTAL CURRENT LIABILITIES	618,575	701,563
LONG-TERM DEBT, less current portion	148,992	161,990
OPERATING LEASE LIABILITIES, less current portion	174,085	176,621
POSTRETIREMENT LIABILITIES, less current portion	13,318	13,319
CONTINGENT CONSIDERATION	100,220	92,900
OTHER LONG-TERM LIABILITIES	34,422	40,553
DEFERRED INCOME TAXES	44,798	55,785
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value, authorized 70,000,000 shares; issued 2024: 30,038,556 shares; 2023: 30,024,125 shares	300	300
Additional paid-in capital	343,102	340,961
Retained earnings	1,267,444	1,272,584
Treasury stock, at cost, 2024: 6,580,818 shares; 2023: 6,460,137 shares	(391,458)	(375,806)
Accumulated other comprehensive income	3,345	4,324
TOTAL STOCKHOLDERS' EQUITY	1,222,733	1,242,363
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 2,357,143	$ 2,485,094