Employee and Retiree Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2018

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)		2018	2017	2018		2017
Service cost	$	2,252	2,037		492		427
Interest cost		6,716	7,261		874		966
Expected return on plan assets		(7,476)	(8,070)		–		–
Amortization of prior service cost (credit)		254	259		(10)		(18)
Recognized actuarial loss		5,197	3,610		–		–
Net periodic benefit expense	$	6,943	5,097		1,356		1,375
	Nine Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)		2018	2017	2018		2017
Service cost	$	6,761	6,099		1,479		1,276
Interest cost		20,160	20,267		2,622		2,899
Expected return on plan assets		(22,435)	(21,730)		–		–
Amortization of prior service cost (credit)		767	767		(29)		(55)
Recognized actuarial loss		15,593	10,673		–		–
Net periodic benefit expense	$	20,846	16,076		4,072		4,120