Pension and Postretirement Benefits (Tables)

3 Months Ended

Mar. 31, 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 March 31,
	2019			2018			2019			2018
	(Dollars in Thousands)
Service cost	$	7,872		$	8,148		$	15		$	22
Interest cost		9,395			8,361			131			125
Expected return on assets		(11,966	)		(10,629	)		—			—
Amortization of:
Prior service cost (credit)		2			26			(190	)		(611	)
Actuarial loss (gain)		3,932			3,296			(118	)		(57	)
Net periodic benefit cost (credit)	$	9,235		$	9,202		$	(162	)	$	(521	)