v3.10.0.1
EMPLOYEE BENEFIT PLANS (Tables)
 6 Months Ended
Jun. 30, 2018
Retirement Benefits [Abstract]  
Schedule of Net Benefit Costs [Table Text Block]
The components of net periodic benefit cost (income) related to our Pension Plans and other postretirement benefit plans were as follows:
 
Pension Plans
 
Other Postretirement Benefit Plans
 
2018
 
2017
 
2018
 
2017
 
(Thousands of Dollars)
For the three months ended June 30:
 
 
 
 
 
 
 
Service cost
$
2,405

 
$
2,239

 
$
126

 
$
113

Interest cost
1,206

 
1,127

 
107

 
108

Expected return on assets
(1,854
)
 
(1,602
)
 
—

 
—

Amortization of prior service credit
(514
)
 
(516
)
 
(286
)
 
(286
)
Amortization of net loss
543

 
371

 
53

 
48

Net periodic benefit cost (income)
$
1,786

 
$
1,619

 
$
—

 
$
(17
)
 
 
 
 
 
 
 
 
For the six months ended June 30:
 
 
 
 
 
 
 
Service cost
$
4,811

 
$
4,478

 
$
252

 
$
226

Interest cost
2,412

 
2,254

 
215

 
216

Expected return on assets
(3,709
)
 
(3,205
)
 
—

 
—

Amortization of prior service credit
(1,028
)
 
(1,031
)
 
(573
)
 
(572
)
Amortization of net loss
1,087

 
742

 
107

 
96

Net periodic benefit cost (income)
$
3,573

 
$
3,238

 
$
1

 
$
(34
)