Employee and Retiree Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2022

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 six-month periods ended June 30, 2022 and 2021.

	Three Months Ended June 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)	2022		2021	2022	2021
Service cost	$	2,129	1,768	292	327
Interest cost	5,139		4,300	574	521
Expected return on plan assets	(7,954)		(6,155)	—	—
Amortization of prior service cost (credit)	579		156	(133)	—
Recognized actuarial loss (gain)	3,822		5,281	(78)	(8)
Net periodic benefit expense	$	3,715	5,350	655	840
	Six Months Ended June 30,
	Pension Benefits			Other Postretirement Benefits
(Thousands of dollars)	2022		2021	2022	2021
Service cost	$	4,258	3,536	584	653
Interest cost	10,382		8,586	1,148	1,042
Expected return on plan assets	(16,092)		(12,288)	—	—
Amortization of prior service cost (credit)	1,179		312	(266)	—
Recognized actuarial loss (gain)	7,644		10,560	(155)	(15)
Net periodic benefit expense	$	7,371	10,706	1,311	1,680