Pension and Postretirement Benefits (Tables)

3 Months Ended

Mar. 31, 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 March 31,
	Pension						Postretirement Benefits
	2015			2014			2015			2014
	(Dollars in Thousands)
Service cost	$	6,290		$	3,730		$	39		$	55
Interest cost		8,112			6,590			230			290
Expected return on assets		(9,104	)		(7,698	)		—			—
Amortization of:
Prior service cost (credit)		105			111			(576	)		(814	)
Actuarial loss (gain)		3,108			1,202			(82	)		(35	)
Termination benefit charge		256			—			—			—
Net periodic benefit cost (credit)	$	8,767		$	3,935		$	(389	)	$	(504	)