CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
CURRENT ASSETS
Cash and cash equivalents	$ 114,280	$ 164,973
Short-term investments	56,838	61,597
Restricted cash	962	1,384
Accounts receivable, less allowances (2016 – $5,437; 2015 – $4,825)	260,643	236,097
Other accounts receivable, less allowances (2016 – $849; 2015 – $1,029)	13,334	6,718
Prepaid expenses	22,124	20,801
Deferred income taxes	39,599	38,443
Prepaid and refundable income taxes	9,909	18,134
Other	4,300	3,936
TOTAL CURRENT ASSETS	521,989	552,083
PROPERTY, PLANT AND EQUIPMENT
Land and structures	305,507	273,839
Revenue equipment	743,860	699,844
Service, office, and other equipment	154,119	145,286
Software	120,877	127,010
Leasehold improvements	27,337	25,419
TOTAL PROPERTY, PLANT AND EQUIPMENT, GROSS	1,351,700	1,271,398
Less allowances for depreciation and amortization	819,174	788,351
PROPERTY, PLANT AND EQUIPMENT, net	532,526	483,047
GOODWILL	108,875	96,465
INTANGIBLE ASSETS, net	80,507	76,787
OTHER LONG-TERM ASSETS	66,095	54,527
TOTAL ASSETS	1,309,992	1,262,909
CURRENT LIABILITIES
Accounts payable	133,301	130,869
Income taxes payable		91
Accrued expenses	190,024	188,727
Current portion of long-term debt	64,143	44,910
TOTAL CURRENT LIABILITIES	387,468	364,597
LONG-TERM DEBT, less current portion	179,530	167,599
PENSION AND POSTRETIREMENT LIABILITIES	35,848	51,241
OTHER LONG-TERM LIABILITIES	16,790	12,689
DEFERRED INCOME TAXES	91,459	78,055
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value, authorized 70,000,000 shares; issued 2016: 28,174,424 shares; 2015: 27,938,319 shares	282	279
Additional paid-in capital	314,916	309,653
Retained earnings	387,161	376,827
Treasury stock, at cost, 2016: 2,565,399 shares; 2015: 2,080,187 shares	(80,045)	(70,535)
Accumulated other comprehensive loss	(23,417)	(27,496)
TOTAL STOCKHOLDERS' EQUITY	598,897	588,728
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 1,309,992	$ 1,262,909