Noninterest Income and Noninterest Expense - Net periodic benefit cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Pension Plan
Components of net periodic benefit cost
Total net periodic benefit cost	$ 1,846	$ 2,185
Pension Plan | Other noninterest expense
Components of net periodic benefit cost
Interest cost	1,361	1,231
Expected return on plan assets	(783)	(766)
Recognized net actuarial loss (gain)	1,268	1,720
Other Benefits
Components of net periodic benefit cost
Total net periodic benefit cost	258	395
Other Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	215	264
Other Benefits | Other noninterest expense
Components of net periodic benefit cost
Interest cost	144	$ 131
Recognized net actuarial loss (gain)	$ (101)