Pension and Other Postretirement Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2017

Retirement Benefits [Abstract]

Components of net periodic benefit cost (income) for the Corporation's qualified and nonqualified pension plans and nonqualified postretirement benefits plan

The components of net periodic benefit cost for the Corporation’s qualified and nonqualified pension plans and nonqualified postretirement benefit plan are as follows:

	Three Months Ended September 30,						Nine Months Ended September 30,
(Dollars in thousands)	2017			2016			2017			2016
Defined Benefit Pension Plans
Service cost	$	233		$	279		$	700		$	834
Interest cost	1,302			1,357			3,906			4,072
Contractual termination cost	—			32			—			32
Expected return on plan assets	(2,216		)	(2,141		)	(6,650		)	(6,422		)
Amortization of unrecognized net loss	578			585			1,734			1,729
Settlement(1)	322			—			322			—
Net periodic benefit cost (income)	$	219		$	112		$	12		$	245
Postretirement Benefit Plan
Service cost	$	1		$	2		$	4		$	7
Interest cost	24			33			70			99
Amortization of prior service cost	—			29			—			88
Amortization of unrecognized net gain	(41		)	(24		)	(121		)	(75		)
Net periodic benefit cost (income)	$	(16	)	$	40		$	(47	)	$	119