Pension and Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2015

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
	2015			2014			2015			2014
	(Dollars in Thousands)
Service cost	$	5,513		$	3,092		$	34		$	51
Interest cost		8,213			5,624			229			305
Expected return on assets		(8,887	)		(6,677	)		—			—
Amortization of:
Prior service cost (credit)		101			96			(570	)		(887	)
Actuarial loss (gain)		7,351			877			(77	)		(73	)
Special termination benefit		1,206			—			—			—
Net periodic benefit cost (credit)	$	13,497		$	3,012		$	(384	)	$	(604	)

	Six Months Ended June 30,
	Pension						Postretirement Benefits
	2015			2014			2015			2014
	(Dollars in Thousands)
Service cost	$	11,505		$	7,131		$	68		$	93
Interest cost		16,575			12,971			464			559
Expected return on assets		(18,190	)		(15,400	)		—			—
Amortization of:
Prior service cost (credit)		211			223			(1,150	)		(1,627	)
Actuarial loss (gain)		10,700			2,022			(154	)		(133	)
Special termination benefit		1,462			—			—			—
Net periodic benefit cost (credit)	$	22,263		$	6,947		$	(772	)	$	(1,108	)