Employee and Retiree Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2021

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, 2021 and 2020.

	Three Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)	2021		2020	2021	2020
Service cost	$	1,770	1,664	328	342
Interest cost	4,258		4,827	521	612
Expected return on plan assets	(6,038)		(5,773)	—	—
Amortization of prior service cost (credit)	155		149	—	—
Recognized actuarial loss	5,269		5,690	(8)	(24)
Net periodic benefit expense	$	5,414	6,557	841	930
	Nine Months Ended September 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)	2021		2020	2021	2020
Service cost	$	5,306	5,996	981	1,235
Interest cost	12,844		16,381	1,563	2,200
Expected return on plan assets	(18,326)		(18,414)	—	—
Amortization of prior service cost (credit)	467		515	—	—
Recognized actuarial loss	15,829		14,223	(23)	(24)
Net periodic benefit expense	$	16,120	18,701	2,521	3,411
Other - curtailment	—		586	—	(1,825)
Other - special termination benefits	—		8,435	—	—
Total net periodic benefit expense	$	16,120	27,722	2,521	1,586