Pension and Postretirement Benefits (Tables)

9 Months Ended

Sep. 30, 2019

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:

	Pension						Postretirement Benefits
	Three Months Ended September 30,
	2019			2018			2019			2018
	(Dollars in Thousands)
Service cost	$	7,711		$	7,911		$	15		$	19
Interest cost		9,424			8,307			131			130
Expected return on assets		(11,929	)		(11,516	)		—			—
Amortization of:
Prior service cost (credit)		2			27			(190	)		(519	)
Actuarial loss (gain)		3,927			3,206			(114	)		(53	)
Settlement charge		—			2,692			—			—
Net periodic benefit cost (credit)	$	9,135		$	10,627		$	(158	)	$	(423	)

	Pension						Postretirement Benefits
	Nine Months Ended September 30,
	2019			2018			2019			2018
	(Dollars in Thousands)
Service cost	$	23,133		$	23,732		$	44		$	58
Interest cost		28,280			24,921			437			389
Expected return on assets		(35,864	)		(34,549	)		—			—
Amortization of:
Prior service cost (credit)		5			77			(571	)		(1,556	)
Actuarial loss (gain)		11,852			9,621			(387	)		(158	)
Settlement charge		—			2,692			—			—
Net periodic benefit cost (credit)	$	27,406		$	26,494		$	(477	)	$	(1,267	)