Retirement Plans (Tables)

3 Months Ended

Mar. 31, 2018

Defined Benefit Plan [Abstract]

Net period benefit cost for the pension and postretirement plans

The components of net periodic benefit cost for the RAP, Bank Mutual Pension Plan, and \Postretirement Plan for three months ended March 31, 2018 and 2017 were as follows.

	Three Months Ended March 31,
	2018			2017
	($ in Thousands)
Components of Net Periodic Benefit Cost
RAP
Service cost	$	1,893		$	1,781
Interest cost	1,660			1,756
Expected return on plan assets	(4,755		)	(4,881		)
Amortization of prior service cost	(19		)	(19		)
Amortization of actuarial loss	463			488
Total net pension cost	$	(759	)	$	(875	)
Bank Mutual Pension Plan (a)
Interest cost	$	433		N/A
Expected return on plan assets	(532		)	N/A
Total net pension cost	$	(99	)	N/A
Postretirement Plan (b)
Interest cost	$	26		$	24
Amortization of prior service cost	(19		)	(19		)
Amortization of actuarial loss	2			—
Total net periodic benefit cost	$	9		$	5