Employee and Retiree Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2020

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Expense

The table that follows provides the components of net periodic benefit expense for the three-month and nine-month periods ended September 30, 2020 and 2019.

	Three Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)	2020		2019	2020	2019
Service cost	$	1,664	2,064	342	421
Interest cost	4,827		7,151	612	945
Expected return on plan assets	(5,773)		(6,455)	—	—
Amortization of prior service cost (credit)	149		248	—	(98)
Recognized actuarial loss	5,690		3,516	(24)	—
Net periodic benefit expense	$	6,557	6,524	930	1,268
	Nine Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)	2020		2019	2020	2019
Service cost	$	5,996	6,188	1,235	1,261
Interest cost	16,381		21,402	2,200	2,833
Expected return on plan assets	(18,414)		(19,285)	—	—
Amortization of prior service cost (credit)	515		741	—	(293)
Recognized actuarial loss	14,223		10,538	(24)	—
Net periodic benefit expense	18,701		19,584	3,411	3,801
Other - curtailment	586		—	(1,825)	—
Other - special termination benefits	8,435		—	—	—
Total net periodic benefit expense	$	27,722	19,584	1,586	3,801