Employee and Retiree Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2017

Employee and Retiree Benefit Plans [Abstract]

Components of Net Periodic Benefit Expense

	Three Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2017	2016	2017		2016
Service cost	$	2,037	2,610		427		674
Interest cost		7,261	5,913		966		1,109
Expected return on plan assets		(8,070)	(6,626)		–		–
Amortization of prior service cost (credit)		259	323		(18)		(21)
Amortization of transitional asset		–	–		–		2
Recognized actuarial loss		3,610	3,617		–		38
Net periodic benefit expense	$	5,097	5,837		1,375		1,802
	Nine Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2017	2016	2017		2016
Service cost	$	6,099	8,533		1,276		2,022
Interest cost		20,267	20,386		2,899		3,324
Expected return on plan assets		(21,730)	(21,709)		–		–
Amortization of prior service cost (credit)		767	963		(55)		(62)
Amortization of transitional asset		–	–		–		4
Recognized actuarial loss		10,673	10,864		–		113
Curtailments		–	822		–		(19)
Net periodic benefit expense	$	16,076	19,859		4,120		5,382