Noninterest Income and Noninterest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating lease income related to lease payments
Operating lease income	$ 1,700	$ 1,600	$ 5,000	$ 4,700
Lease income related to variable lease payments	1,600	1,400	4,600	4,300
Pension Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	2,246	1,907	6,616	5,619
Pension Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	1,292	1,639	3,754	4,881
Expected return on plan assets	(766)	(1,206)	(2,298)	(3,594)
Recognized net actuarial loss (gain)	1,720	1,474	5,160	4,332
Other Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	334	259	1,124	887
Other Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	218	195	746	573
Other Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	$ 116	156	$ 378	484
Prior service credit		(12)		(38)
Recognized net actuarial loss (gain)		$ (80)		$ (132)