Pension and Postretirement Benefits (Tables)

9 Months Ended

Sep. 30, 2018

Compensation And Retirement Disclosure [Abstract]

Schedule of Components of Net Periodic Benefit Cost (Credit)

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

	Three-Months Ended September 30,
	Pension						Postretirement Benefits
	2018			2017			2018			2017
	(Dollars in Thousands)
Service cost	$	7,911		$	7,457		$	19		$	20
Interest cost		8,307			9,729			130			182
Expected return on assets		(11,516	)		(10,691	)		—			—
Amortization of:
Prior service cost (credit)		27			34			(519	)		(436	)
Actuarial loss (gain)		3,206			3,604			(53	)		(91	)
Settlement charge		2,692			—			—			—
Net periodic benefit cost (credit)	$	10,627		$	10,133		$	(423	)	$	(325	)

	Nine-Months Ended September 30,
	Pension						Postretirement Benefits
	2018			2017			2018			2017
	(Dollars in Thousands)
Service cost	$	23,732		$	20,060		$	58		$	60
Interest cost		24,921			27,074			389			547
Expected return on assets		(34,549	)		(29,818	)		—			—
Amortization of:
Prior service cost (credit)		77			237			(1,556	)		(1,307	)
Actuarial loss (gain)		9,621			10,643			(158	)		(273	)
Settlement charge		2,692			—			—			—
Net periodic benefit cost (credit)	$	26,494		$	28,196		$	(1,267	)	$	(973	)