Retirement Plans (Tables)

9 Months Ended

Sep. 30, 2017

Defined Benefit Plan [Abstract]

Net period benefit cost for the pension and postretirement plans

The components of net periodic benefit cost for the RAP and Postretirement Plan for three and nine months ended September 30, 2017 and 2016 were as follows.

	Three Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	($ in Thousands)
Components of Net Periodic Benefit Cost
RAP
Service cost	$	1,713		$	1,636		$	5,276		$	5,086
Interest cost	1,795			1,781			5,307			5,341
Expected return on plan assets	(4,929		)	(5,085		)	(14,692		)	(15,215		)
Amortization of prior service cost	(19		)	(80		)	(56		)	(55		)
Amortization of actuarial loss	619			621			1,594			1,586
Total net pension cost	$	(821	)	$	(1,127	)	$	(2,571	)	$	(3,257	)
Postretirement Plan
Interest cost	$	26		$	35		$	74		$	107
Amortization of prior service cost	(19		)	—			(57		)	—
Amortization of actuarial loss	2			—			2			—
Total net periodic benefit cost	$	9		$	35		$	19		$	107