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EMPLOYEE BENEFIT PLANS (Tables)
3 Months Ended
Mar. 31, 2017
Employee Benefit Plans [Line Items]  
Schedule of Net Benefit Costs [Table Text Block]
The following tables set forth the components of net periodic benefit cost for our pension and other postemployment benefit plans for the periods indicated:
 
Pension Benefits
 
Three Months Ended
 
March 31,
 
2017
2016
 
(Thousands of dollars)
Components of net periodic benefit cost
 
 
Service cost
$
3,044

$
3,014

Interest cost
10,113

11,387

Expected return on assets
(14,624
)
(15,296
)
Amortization of net loss
9,027

8,886

Net periodic benefit cost
$
7,560

$
7,991


 
Other Postemployment Benefits
 
Three Months Ended
 
March 31,
 
2017
2016
 
(Thousands of dollars)
Components of net periodic benefit cost
 
 
Service cost
$
627

$
638

Interest cost
2,472

2,627

Expected return on assets
(3,147
)
(3,071
)
Amortization of unrecognized prior service cost
(1,149
)
(908
)
Amortization of net loss
1,621

1,151

Net periodic benefit cost
$
424

$
437