Noninterest Income and Noninterest Expense - Net periodic benefit cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension Plan
Components of net periodic benefit cost
Interest cost	$ 1,906	$ 2,059
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense
Expected return on plan assets	$ (878)	$ (883)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense
Recognized net actuarial loss (gain)	$ 503	$ 719
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense
Total net periodic benefit cost	$ 1,531	$ 1,895
Other Benefits
Components of net periodic benefit cost
Interest cost	$ 211	$ 220
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense
Recognized net actuarial loss (gain)	$ (322)	$ (379)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense
Total net periodic benefit cost	$ 26	$ (12)
Other Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	$ 137	$ 147