CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
CURRENT ASSETS
Cash and cash equivalents	$ 352,165	$ 201,909
Short-term investments	178,810	116,579
Accounts receivable, less allowances (2020 - $6,111; 2019 - $5,448)	278,783	282,579
Other accounts receivable, less allowances (2020 - $646; 2019 - $476)	15,276	18,774
Prepaid expenses	33,806	30,377
Prepaid and refundable income taxes	6,231	9,439
Other	4,460	4,745
TOTAL CURRENT ASSETS	869,531	664,402
PROPERTY, PLANT AND EQUIPMENT
Land and structures	343,527	342,122
Revenue equipment	885,949	896,020
Service, office, and other equipment	230,163	233,354
Software	154,749	151,068
Leasehold improvements	11,022	10,383
TOTAL PROPERTY, PLANT AND EQUIPMENT, Gross	1,625,410	1,632,947
Less allowances for depreciation and amortization	961,950	949,355
PROPERTY, PLANT AND EQUIPMENT, net	663,460	683,592
GOODWILL	88,320	88,320
INTANGIBLE ASSETS, net	57,873	58,832
OPERATING RIGHT-OF-USE ASSETS	73,324	68,470
DEFERRED INCOME TAXES	8,145	7,725
OTHER LONG-TERM ASSETS	73,703	79,866
TOTAL ASSETS	1,834,356	1,651,207
CURRENT LIABILITIES
Accounts payable	127,625	134,374
Income taxes payable	31	12
Accrued expenses	217,678	232,321
Current portion of long-term debt	56,977	57,305
Current portion of operating lease liabilities	20,542	20,265
TOTAL CURRENT LIABILITIES	422,853	444,277
LONG-TERM DEBT, less current portion	476,945	266,214
OPERATING LEASE LIABILITIES, less current portion	56,716	52,277
POSTRETIREMENT LIABILITIES, less current portion	20,411	20,294
OTHER LONG-TERM LIABILITIES	35,058	38,892
DEFERRED INCOME TAXES	63,167	66,210
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value, authorized 70,000,000 shares; issued 2020: 28,817,109 shares, 2019: 28,810,902 shares	288	288
Additional paid-in capital	336,064	333,943
Retained earnings	532,858	533,187
Treasury stock, at cost, 2020: 3,554,639 shares; 2019: 3,404,639 shares	(107,740)	(104,578)
Accumulated other comprehensive income (loss)	(2,264)	203
TOTAL STOCKHOLDERS' EQUITY	759,206	763,043
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 1,834,356	$ 1,651,207