Noninterest Income and Noninterest Expense - Net periodic benefit cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pension Plan
Components of net periodic benefit cost
Interest cost	$ 2,059	$ 1,361	$ 4,118	$ 2,722
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	$ (882)	$ (782)	$ (1,765)	$ (1,565)
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)	$ 719	$ 1,269	$ 1,438	$ 2,537
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	$ 1,896	$ 1,848	$ 3,791	$ 3,694
Other Benefits
Components of net periodic benefit cost
Interest cost	$ 220	$ 143	$ 440	$ 287
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)	$ (379)	$ (101)	$ (758)	$ (202)
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	$ (12)	$ 256	$ (24)	$ 514
Other Benefits | Salaries and employee benefits
Components of net periodic benefit cost
Service cost	$ 147	$ 214	$ 294	$ 429