Noninterest Income and Noninterest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating lease income related to lease payments
Operating lease income	$ 1,600	$ 1,600	$ 3,300	$ 3,100
Lease income related to variable lease payments	1,500	1,400	3,000	2,900
Pension Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	2,185	1,856	4,370	3,712
Pension Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	1,231	1,621	2,462	3,242
Expected return on plan assets	(766)	(1,194)	(1,532)	(2,388)
Recognized net actuarial loss (gain)	1,720	1,429	3,440	2,858
Other Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	395	314	790	628
Other Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	264	189	528	378
Other Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	$ 131	164	$ 262	328
Prior service credit		(13)		(26)
Recognized net actuarial loss (gain)		$ (26)		$ (52)