Retirement Plans, Components of Net Periodic Benefit Cost for the Pension and Postretirement Tables (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
RAP
Net period benefit cost for the pension and postretirement plans
Service cost	$ 1,598	$ 1,885	$ 5,448	$ 5,670
Interest cost	2,489	1,682	7,314	5,002
Expected return on plan assets	(6,099)	(4,777)	(18,249)	(14,287)
Amortization of prior service cost	(18)	(18)	(55)	(56)
Amortization of actuarial loss	230	549	360	1,474
Total net periodic pension cost	(1,800)	(680)	(5,183)	(2,197)
Bank Mutual Pension Plan
Net period benefit cost for the pension and postretirement plans
Interest cost		654		1,737
Expected return on plan assets		(1,220)		(2,812)
Total net periodic pension cost		(566)		(1,075)
Postretirement Plan
Net period benefit cost for the pension and postretirement plans
Interest cost	26	27	78	80
Amortization of prior service cost	(19)	(19)	(56)	(56)
Amortization of actuarial loss	(1)	2	(3)	6
Total net periodic pension cost	$ 6	$ 11	$ 19	$ 30