Retirement Benefits (Tables)

9 Months Ended

Sep. 30, 2020

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost

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

	Three Months Ended				Nine Months Ended
	Sept. 30, 2020		Sept. 30, 2019		Sept. 30, 2020		Sept. 30, 2019
	(Dollars in thousands)
Service cost	$	2,983	$	2,871	$	9,958	$	9,383
Interest cost	5,816		7,149		17,236		21,241
Expected return on plan assets	(18,104)		(15,200)		(54,091)		(45,425)
Amortization of prior service cost	43		46		154		86
Amortization of actuarial losses	2,993		4,084		8,862		12,324
Net periodic benefit credit	$	(6,269)	$	(1,050)	$	(17,881)	$	(2,391)

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

	Three Months Ended				Nine Months Ended
	Sept. 30, 2020		Sept. 30, 2019		Sept. 30, 2020		Sept. 30, 2019
	(Dollars in thousands)
Service cost	$	18	$	16	$	66	$	60
Interest cost	142		200		425		569
Amortization of prior service credit	(487)		(586)		(1,454)		(1,749)
Amortization of actuarial gains	(115)		(33)		(254)		(366)
Net periodic benefit credit	$	(442)	$	(403)	$	(1,217)	$	(1,486)