Retirement Benefits (Tables)

9 Months Ended

Sep. 30, 2023

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost (Credit)

The components of the net periodic pension benefit cost (credit) were as follows:

	Three Months Ended				Nine Months Ended
	Sept. 30, 2023		Sept. 30, 2022		Sept. 30, 2023		Sept. 30, 2022
	(Dollars in thousands)
Service cost	$	1,962	$	2,937	$	6,425	$	9,507
Interest cost	8,617		5,131		26,050		15,430
Expected return on plan assets	(10,211)		(17,220)		(30,587)		(51,849)
Amortization of prior service cost	29		62		82		170
Amortization of actuarial losses	2,845		1,370		8,729		3,682
Net periodic benefit cost (credit)	$	3,242	$	(7,720)	$	10,699	$	(23,060)

The components of the net periodic other postretirement benefit credit were as follows:

	Three Months Ended				Nine Months Ended
	Sept. 30, 2023		Sept. 30, 2022		Sept. 30, 2023		Sept. 30, 2022
	(Dollars in thousands)
Service cost	$	12	$	5	$	38	$	56
Interest cost	181		96		559		314
Amortization of prior service credit	(237)		(415)		(705)		(1,247)
Amortization of actuarial gains	(141)		(75)		(464)		(229)
Net periodic benefit credit	$	(185)	$	(389)	$	(572)	$	(1,106)