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ACCRUED LIABILITIES
12 Months Ended
Dec. 31, 2017
Accrued Liabilities, Current [Abstract]  
ACCRUED LIABILITIES
ACCRUED LIABILITIES
Accrued liabilities consisted of the following:
 
December 31,
 
2017
 
2016
 
(Thousands of Dollars)
Employee wages and benefit costs
$
16,963

 
$
30,807

Unearned income
18,243

 
14,355

Other
26,372

 
15,323

Accrued liabilities
$
61,578

 
$
60,485