Noninterest Income and Noninterest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Leases
Operating lease income	$ 1,600	$ 1,500	$ 3,100	$ 3,000
Lease income related to variable lease payments	1,400	1,300	2,900	2,600
Amortization of software expenses recorded in other noninterest expense
Amortization of software expenses	1,400	1,000	2,600	2,200
Pension Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	1,856	2,430	3,712	4,860
Pension Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost		17		34
Pension Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	1,621	2,044	3,242	4,088
Expected return on plan assets	(1,194)	(1,195)	(2,388)	(2,390)
Recognized net actuarial loss (gain)	1,429	1,564	2,858	3,128
Other Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	314	182	628	364
Other Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	189	159	378	318
Other Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	164	206	328	412
Prior service credit	(13)	(107)	(26)	(214)
Recognized net actuarial loss (gain)	$ (26)	$ (76)	$ (52)	$ (152)