CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
CURRENT ASSETS
Cash and cash equivalents	$ 203,319	$ 158,264
Short-term investments	162,487	167,662
Accounts receivable, less allowances (2023 - $11,585; 2022 - $13,892)	470,440	517,494
Other accounts receivable, less allowances (2023 - $721; 2022 - $713)	11,485	11,016
Prepaid expenses	41,061	39,484
Prepaid and refundable income taxes	16,351	19,239
Current assets of discontinued operations		64,736
Other	11,887	11,888
TOTAL CURRENT ASSETS	917,030	989,783
PROPERTY, PLANT AND EQUIPMENT
Land and structures	418,011	401,840
Revenue equipment	1,039,771	1,038,832
Service, office, and other equipment	303,698	298,234
Software	170,523	167,164
Leasehold improvements	24,693	23,466
TOTAL PROPERTY, PLANT AND EQUIPMENT, Gross	1,956,696	1,929,536
Less allowances for depreciation and amortization	1,151,396	1,129,366
PROPERTY, PLANT AND EQUIPMENT, net	805,300	800,170
GOODWILL	304,753	304,753
INTANGIBLE ASSETS, net	110,622	113,733
OPERATING RIGHT-OF-USE ASSETS	189,610	166,515
DEFERRED INCOME TAXES	7,287	6,342
LONG-TERM ASSETS OF DISCONTINUED OPERATIONS		11,097
OTHER LONG-TERM ASSETS	96,991	101,893
TOTAL ASSETS	2,431,593	2,494,286
CURRENT LIABILITIES
Accounts payable	253,578	269,854
Income taxes payable	19,460	16,017
Accrued expenses	278,658	338,457
Current portion of contingent consideration	43,390
Current portion of long-term debt	64,491	66,252
Current portion of operating lease liabilities	28,466	26,225
Current liabilities of discontinued operations		51,665
TOTAL CURRENT LIABILITIES	688,043	768,470
LONG-TERM DEBT, less current portion	185,961	198,371
OPERATING LEASE LIABILITIES, less current portion	170,253	147,828
POSTRETIREMENT LIABILITIES, less current portion	12,169	12,196
LONG-TERM LIABILITIES OF DISCONTINUED OPERATIONS		781
CONTINGENT CONSIDERATION, less current portion	83,650	112,000
OTHER LONG-TERM LIABILITIES	34,248	42,745
DEFERRED INCOME TAXES	51,410	60,494
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value, authorized 70,000,000 shares; issued 2023: 29,808,628 shares; 2022: 29,758,716 shares	298	298
Additional paid-in capital	340,481	339,582
Retained earnings	1,157,061	1,088,693
Treasury stock, at cost, 2023: 5,683,472 shares; 2022: 5,529,383 shares	(298,367)	(284,275)
Accumulated other comprehensive income	6,386	7,103
TOTAL STOCKHOLDERS' EQUITY	1,205,859	1,151,401
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 2,431,593	$ 2,494,286