Retirement Benefits

9 Months Ended

Sep. 30, 2015

Compensation and Retirement Disclosure [Abstract]

Retirement Benefits

Retirement Benefits

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

	Three Months Ended						Nine Months Ended
	Sept. 30, 2015			Sept. 30, 2014			Sept. 30, 2015			Sept. 30, 2014
	(Dollars in thousands)
Service cost	$	3,688		$	3,392		$	11,689		$	10,163
Interest cost	6,753			7,399			21,044			22,248
Expected return on plan assets	(15,692		)	(14,312		)	(47,045		)	(43,000		)
Amortization of prior service cost	264			272			778			891
Amortization of actuarial losses	627			154			4,293			588
Curtailment gain	(482		)	—			(482		)	—
Net periodic benefit credit	$	(4,842	)	$	(3,095	)	$	(9,723	)	$	(9,110	)

The components of the net periodic other postretirement benefits costs were as follows:

	Three Months Ended						Nine Months Ended
	Sept. 30, 2015			Sept. 30, 2014			Sept. 30, 2015			Sept. 30, 2014
	(Dollars in thousands)
Service cost	$	56		$	138		$	335		$	402
Interest cost	256			420			965			1,245
Amortization of prior service credit	(817		)	(726		)	(2,289		)	(2,154		)
Amortization of actuarial gains	(133		)	(75		)	(260		)	(246		)
Net periodic benefit credit	$	(638	)	$	(243	)	$	(1,249	)	$	(753	)