Pension and Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2016

Compensation And Retirement Disclosure [Abstract]

Schedule of Components of Net Periodic Benefit Cost

The estimated components of the recorded net periodic benefit cost (credit) for pension and postretirement benefits are as follows:

	Three Months Ended June 30,
	Pension						Postretirement Benefits
	2016			2015			2016			2015
	(Dollars in Thousands)
Service cost	$	5,776		$	5,513		$	24		$	34
Interest cost		9,331			8,213			259			229
Expected return on assets		(9,822	)		(8,887	)		—			—
Amortization of:
Prior service cost (credit)		91			101			(609	)		(570	)
Actuarial loss (gain)		3,146			7,351			(139	)		(77	)
Special termination benefit		638			1,206			(8	)		—
Net periodic benefit cost (credit)	$	9,160		$	13,497		$	(473	)	$	(384	)

	Six Months Ended June 30,
	Pension						Postretirement Benefits
	2016			2015			2016			2015
	(Dollars in Thousands)
Service cost	$	11,082		$	11,505		$	43		$	68
Interest cost		17,938			16,575			432			464
Expected return on assets		(18,848	)		(18,190	)		—			—
Amortization of:
Prior service cost (credit)		175			211			(981	)		(1,150	)
Actuarial loss (gain)		6,036			10,700			(249	)		(154	)
Settlement charge		59			—			—			—
Special termination benefit		764			1,462			(8	)		—
Net periodic benefit cost (credit)	$	17,206		$	22,263		$	(763	)	$	(772	)