Retirement Benefits (Tables)

3 Months Ended

Mar. 31, 2016

Compensation and Retirement Disclosure [Abstract]

Components of Net Periodic Benefit Cost

The components of the net periodic pension benefit credit for the three months ended March 31 were as follows:

	2016			2015
	(Dollars in thousands)
Service cost	$	3,313		$	4,050
Interest cost	6,434			7,149
Expected return on plan assets	(14,583		)	(15,655		)
Amortization of prior service cost	151			246
Amortization of actuarial losses	2,083			1,833
Net periodic benefit credit	$	(2,602	)	$	(2,377	)

The components of the net periodic other postretirement benefits credit for the three months ended March 31 were as follows:

	2016			2015
	(Dollars in thousands)
Service cost	$	67		$	143
Interest cost	254			360
Amortization of prior service credit	(850		)	(736		)
Amortization of actuarial gains	(118		)	(64		)
Net periodic benefit credit	$	(647	)	$	(297	)