Noninterest Income and Noninterest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Leases
Operating lease income	$ 1,600	$ 1,500	$ 4,700	$ 4,400
Lease income related to variable lease payments	1,400	1,400	4,300	4,000
Pension Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	1,907	2,431	5,619	7,291
Pension Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost		18		52
Pension Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	1,639	2,044	4,881	6,132
Expected return on plan assets	(1,206)	(1,195)	(3,594)	(3,585)
Recognized net actuarial loss (gain)	1,474	1,564	4,332	4,692
Other Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	259	180	887	544
Other Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	195	160	573	478
Other Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	156	203	484	615
Prior service credit	(12)	(107)	(38)	(321)
Recognized net actuarial loss (gain)	$ (80)	$ (76)	$ (132)	$ (228)