Pension and Postretirement Benefits (Tables)

6 Months Ended

Jun. 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 June 30,
	2019			2018			2019			2018
	(Dollars in Thousands)
Service cost	$	7,617		$	7,684		$	14		$	16
Interest cost		9,300			8,252			125			134
Expected return on assets		(11,824	)		(12,403	)		—			—
Amortization of:
Prior service cost (credit)		1			26			(185	)		(426	)
Actuarial loss (gain)		3,941			3,117			(109	)		(48	)
Net periodic benefit cost (credit)	$	9,035		$	6,676		$	(155	)	$	(324	)

	Pension						Postretirement Benefits
	Six Months Ended June 30,
	2019			2018			2019			2018
	(Dollars in Thousands)
Service cost	$	15,422		$	15,832		$	48		$	38
Interest cost		18,856			16,613			281			259
Expected return on assets		(23,930	)		(23,032	)		—			—
Amortization of:
Prior service cost (credit)		3			52			(399	)		(1,037	)
Actuarial loss (gain)		7,918			6,413			(248	)		(105	)
Net periodic benefit cost (credit)	$	18,269		$	15,878		$	(318	)	$	(845	)