CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
CURRENT ASSETS
Cash and cash equivalents	$ 406,290	$ 201,909
Short-term investments	167,719	116,579
Accounts receivable, less allowances (2020 - $7,130; 2019 - $5,448)	273,135	282,579
Other accounts receivable, less allowances (2020 - $661; 2019 - $476)	16,812	18,774
Prepaid expenses	28,928	30,377
Prepaid and refundable income taxes	4,236	9,439
Other	4,923	4,745
TOTAL CURRENT ASSETS	902,043	664,402
PROPERTY, PLANT AND EQUIPMENT
Land and structures	344,951	342,122
Revenue equipment	891,029	896,020
Service, office, and other equipment	232,058	233,354
Software	155,411	151,068
Leasehold improvements	11,821	10,383
TOTAL PROPERTY, PLANT AND EQUIPMENT, Gross	1,635,270	1,632,947
Less allowances for depreciation and amortization	974,464	949,355
PROPERTY, PLANT AND EQUIPMENT, net	660,806	683,592
GOODWILL	88,320	88,320
INTANGIBLE ASSETS, net	56,915	58,832
OPERATING RIGHT-OF-USE ASSETS	81,069	68,470
DEFERRED INCOME TAXES	7,507	7,725
OTHER LONG-TERM ASSETS	74,100	79,866
TOTAL ASSETS	1,870,760	1,651,207
CURRENT LIABILITIES
Accounts payable	140,632	134,374
Income taxes payable	3,181	12
Accrued expenses	217,020	232,321
Current portion of long-term debt	59,050	57,305
Current portion of operating lease liabilities	19,769	20,265
TOTAL CURRENT LIABILITIES	439,652	444,277
LONG-TERM DEBT, less current portion	473,850	266,214
OPERATING LEASE LIABILITIES, less current portion	65,249	52,277
POSTRETIREMENT LIABILITIES, less current portion	20,448	20,294
OTHER LONG-TERM LIABILITIES	36,077	38,892
DEFERRED INCOME TAXES	60,393	66,210
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value, authorized 70,000,000 shares; issued 2020: 28,958,258 shares, 2019: 28,810,902 shares	290	288
Additional paid-in capital	337,942	333,943
Retained earnings	546,689	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)	(2,090)	203
TOTAL STOCKHOLDERS' EQUITY	775,091	763,043
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 1,870,760	$ 1,651,207