Retirement Benefits (Tables)

9 Months Ended

Sep. 30, 2018

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, 2018			Sept. 30, 2017			Sept. 30, 2018			Sept. 30, 2017
	(Dollars in thousands)
Service cost	$	3,411		$	3,532		$	10,842		$	9,967
Interest cost	6,348			6,482			18,953			19,114
Expected return on plan assets	(17,137		)	(15,832		)	(51,382		)	(47,258		)
Amortization of prior service cost	34			75			103			235
Amortization of actuarial losses	1,877			1,501			5,450			5,208
Net periodic benefit credit	$	(5,467	)	$	(4,242	)	$	(16,034	)	$	(12,734	)

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

	Three Months Ended						Nine Months Ended
	Sept. 30, 2018			Sept. 30, 2017			Sept. 30, 2018			Sept. 30, 2017
	(Dollars in thousands)
Service cost	$	15		$	9		$	78		$	79
Interest cost	158			168			483			520
Amortization of prior service cost (credit)	561			(857		)	(738		)	(2,564		)
Amortization of actuarial gains	(167		)	(172		)	(405		)	(447		)
Net periodic benefit cost (credit)	$	567		$	(852	)	$	(582	)	$	(2,412	)