Benefit Plans - Net periodic benefit cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Funded Plan
Components of net periodic benefit cost
Interest cost	$ 2,261	$ 2,946	$ 3,808
Expected return on plan assets	(3,044)	(4,800)	(4,585)
Recognized net actuarial loss (gain)	1,609	1,421	3,714
Total net periodic benefit cost	826	(433)	2,937
Pension Plan
Components of net periodic benefit cost
Interest cost	5,065	6,519
Total net periodic benefit cost	8,982	7,525	10,685
Pension Plan | Salaries and employee benefits
Components of net periodic benefit cost
Service cost			14
Pension Plan | Other noninterest expense
Components of net periodic benefit cost
Interest cost	5,065	6,519	8,261
Expected return on plan assets	(3,044)	(4,800)	(4,585)
Recognized net actuarial loss (gain)	6,961	5,806	6,995
Other Benefits
Components of net periodic benefit cost
Service cost	874	768
Interest cost	515	640
Total net periodic benefit cost	1,341	1,146	704
Other Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	874	768	710
Other Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	515	640	808
Prior service credit		(51)	(429)
Recognized net actuarial loss (gain)	$ (48)	$ (211)	$ (385)