Pension and Other Postretirement Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2016

Compensation and Retirement Disclosure [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)	2016			2015			2016			2015
Defined Benefit Pension Plans
Service cost	$	279		$	273		$	834		$	818
Interest cost	1,357			1,331			4,072			3,995
Contractual termination cost	32			—			32			—
Expected return on plan assets	(2,141		)	(2,161		)	(6,422		)	(6,483		)
Amortization of prior service credit	—			(2		)	—			(4		)
Amortization of unrecognized net loss	585			1,057			1,729			3,169
Net periodic benefit cost	$	112		$	498		$	245		$	1,495
Postretirement Benefit Plan
Service cost	$	2		$	4		$	7		$	12
Interest cost	33			33			99			100
Amortization of prior service cost	29			32			88			97
Amortization of unrecognized net gain	(24		)	—			(75		)	(1		)
Net periodic benefit cost	$	40		$	69		$	119		$	208