Retirement Benefits (Tables)

6 Months Ended

Jun. 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				Six Months Ended
	June 30, 2023		June 30, 2022		June 30, 2023		June 30, 2022
	(Dollars in thousands)
Service cost	$	2,234	$	3,270	$	4,463	$	6,570
Interest cost	8,724		5,140		17,433		10,299
Expected return on plan assets	(10,187)		(17,315)		(20,376)		(34,629)
Amortization of prior service cost	25		53		53		108
Amortization of actuarial losses	2,939		1,157		5,884		2,312
Net periodic benefit cost (credit)	$	3,735	$	(7,695)	$	7,457	$	(15,340)

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

	Three Months Ended				Six Months Ended
	June 30, 2023		June 30, 2022		June 30, 2023		June 30, 2022
	(Dollars in thousands)
Service cost	$	12	$	26	$	26	$	51
Interest cost	189		109		378		218
Amortization of prior service credit	(233)		(416)		(468)		(832)
Amortization of actuarial gains	(162)		(77)		(323)		(154)
Net periodic benefit credit	$	(194)	$	(358)	$	(387)	$	(717)