Noninterest Income and Noninterest Expense - Net periodic benefit cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Pension Plan [Member]
Components of net periodic benefit cost
Interest cost	$ 1,950	$ 2,053	$ 5,761	$ 6,171
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Expected return on plan assets	$ (878)	$ (883)	$ (2,634)	$ (2,648)
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	Other Noninterest Expense	Other Noninterest Expense
Recognized net actuarial loss (gain)	$ 503	$ 719	$ 1,509	$ 2,157
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	Other Noninterest Expense	Other Noninterest Expense
Total net periodic benefit cost	$ 1,575	$ 1,889	$ 4,636	$ 5,680
Other Postretirement Benefits Plan [Member]
Components of net periodic benefit cost
Interest cost	$ 182	$ 171	$ 604	$ 611
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	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	Other Noninterest Expense	Other Noninterest Expense
Recognized net actuarial loss (gain)	$ (322)	$ (379)	$ (966)	$ (1,137)
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	Other Noninterest Expense	Other Noninterest Expense
Total net periodic benefit cost	$ 15	$ (72)	$ 67	$ (96)
Other Postretirement Benefits Plan [Member] | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	$ 155	$ 136	$ 429	$ 430