Retirement Plans (Tables)

3 Months Ended

Mar. 31, 2017

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]

Net period benefit cost for the pension and postretirement plans

The components of net periodic benefit cost for the RAP and Postretirement Plans for three months ended March 31, 2017 and 2016 were as follows.

	Three Months Ended March 31,
	2017			2016
	($ in Thousands)
Components of Net Periodic Benefit Cost
Pension Plan:
Service cost	$	1,781		$	1,725
Interest cost	1,756			1,780
Expected return on plan assets	(4,881		)	(5,065		)
Amortization of prior service cost	(19		)	13
Amortization of actuarial loss	488			482
Total net pension cost	$	(875	)	$	(1,065	)
Postretirement Plan:
Interest cost	$	24		$	36
Amortization of prior service cost	(19		)	—
Total net periodic benefit cost	$	5		$	36