v3.10.0.1
EMPLOYEE BENEFIT PLANS (Tables)
 9 Months Ended
Sep. 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 September 30:
 
 
 
 
 
 
 
Service cost
$
2,405

 
$
2,239

 
$
126

 
$
115

Interest cost
1,206

 
1,127

 
107

 
107

Expected return on assets
(1,854
)
 
(1,603
)
 
—

 
—

Amortization of prior service credit
(515
)
 
(515
)
 
(286
)
 
(286
)
Amortization of net loss
544

 
371

 
53

 
47

Net periodic benefit cost (income)
$
1,786

 
$
1,619

 
$
—

 
$
(17
)
 
 
 
 
 
 
 
 
For the nine months ended September 30:
 
 
 
 
 
 
 
Service cost
$
7,216

 
$
6,717

 
$
378

 
$
341

Interest cost
3,618

 
3,381

 
322

 
323

Expected return on assets
(5,563
)
 
(4,808
)
 
—

 
—

Amortization of prior service credit
(1,543
)
 
(1,546
)
 
(859
)
 
(858
)
Amortization of net loss
1,631

 
1,113

 
160

 
143

Net periodic benefit cost (income)
$
5,359

 
$
4,857

 
$
1

 
$
(51
)