CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
CURRENT ASSETS
Cash and cash equivalents	$ 64,108	$ 76,620
Short-term investments	37,024	48,339
Accounts receivable, less allowances (2022 - $15,737; 2021 - $13,226)	676,200	582,344
Other accounts receivable, less allowances (2022 - $697; 2021 - $690)	22,109	13,094
Prepaid expenses	42,688	40,104
Prepaid and refundable income taxes	9,010	9,654
Other	9,440	5,898
TOTAL CURRENT ASSETS	860,579	776,053
PROPERTY, PLANT AND EQUIPMENT
Land and structures	352,420	350,694
Revenue equipment	981,317	980,283
Service, office, and other equipment	259,201	251,085
Software	180,641	175,989
Leasehold improvements	17,226	16,931
TOTAL PROPERTY, PLANT AND EQUIPMENT, Gross	1,790,805	1,774,982
Less allowances for depreciation and amortization	1,098,431	1,079,061
PROPERTY, PLANT AND EQUIPMENT, net	692,374	695,921
GOODWILL	299,008	300,337
INTANGIBLE ASSETS, net	123,363	126,580
OPERATING RIGHT-OF-USE ASSETS	125,988	106,686
DEFERRED INCOME TAXES	5,324	5,470
OTHER LONG-TERM ASSETS	103,063	101,629
TOTAL ASSETS	2,209,699	2,112,676
CURRENT LIABILITIES
Accounts payable	340,966	311,401
Income taxes payable	8,364	12,087
Accrued expenses	276,888	305,851
Current portion of long-term debt	89,766	50,615
Current portion of operating lease liabilities	24,127	22,740
TOTAL CURRENT LIABILITIES	740,111	702,694
LONG-TERM DEBT, less current portion	168,912	174,917
OPERATING LEASE LIABILITIES, less current portion	106,463	88,835
POSTRETIREMENT LIABILITIES, less current portion	16,710	16,733
OTHER LONG-TERM LIABILITIES	130,471	135,537
DEFERRED INCOME TAXES	63,860	64,893
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value, authorized 70,000,000 shares; issued 2022: 29,384,711 shares, 2021: 29,359,597 shares	294	294
Additional paid-in capital	344,429	318,033
Retained earnings	868,905	801,314
Treasury stock, at cost, 2022: 4,900,512 shares; 2021: 4,492,514 shares	(235,779)	(194,273)
Accumulated other comprehensive income	5,323	3,699
TOTAL STOCKHOLDERS' EQUITY	983,172	929,067
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 2,209,699	$ 2,112,676