Retirement Benefit Plans (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Interest credit under cash balance plan	0.03
Employer matching contribution, percent of match, maximum	5.00%
Defined benefit plan, service cost and interest cost			$ 3,300,000
Defined benefit plan, unamortized net loss			$ 7,200,000
Defined benefit plan, benefit obligation from lump sum payment to total benefit obligation ratio			8.06%
Defined benefit plan, net periodic benefit cost, loss due to settlement			$ 577,000
Employees' Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Assumptions used calculating benefit obligation, interest rate to annuitize cash balance account				5.50%
Defined benefit plan, increase in benefit payable, percent	3.00%
Defined benefit plan, benefit obligation, increase (decrease) for plan amendment	$ 351,638
Defined benefit plan, amortization of service cost	9 years 8 months 12 days
Net Periodic Benefit Cost
Service Cost	$ 466,000	$ 413,000
Interest Cost	525,000	530,000
Expected Return on Plan Assets	(932,000)	(857,000)
Amortization of Prior Service Cost	33,000	16,000
Amortization of Net Loss (Gain)	0	36,000
Net Periodic Benefit Cost	92,000	138,000
Plan Contributions During the Period	0	0
Estimated Future Contributions in the Current Fiscal Year	$ 0
Select Executive Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Assumptions used calculating benefit obligation, interest rate to annuitize cash balance account				5.76%
Defined benefit plan, amortization of service cost	12 years 6 months
Defined benefit plan, benefit obligation, period increase (decrease)	$ 122,797
Net Periodic Benefit Cost
Service Cost	17,000	163,000
Interest Cost	158,000	62,000
Expected Return on Plan Assets	0	0
Amortization of Prior Service Cost	10,000	10,000
Amortization of Net Loss (Gain)	21,000	18,000
Net Periodic Benefit Cost	206,000	253,000
Plan Contributions During the Period	127,000	116,000
Estimated Future Contributions in the Current Fiscal Year	382,000
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Assumptions used calculating benefit obligation, interest rate to annuitize cash balance account				5.83%
Net Periodic Benefit Cost
Service Cost	15,000	18,000
Interest Cost	81,000	87,000
Expected Return on Plan Assets	0	0
Amortization of Prior Service Cost	26,000	26,000
Amortization of Net Loss (Gain)	(87,000)	(79,000)
Net Periodic Benefit Cost	35,000	52,000
Plan Contributions During the Period	27,000	$ 27,000
Estimated Future Contributions in the Current Fiscal Year	$ 82,000
Prior to January 1, 2003 | Minimum
Defined Benefit Plan Disclosure [Line Items]
Service credits, percent of eligible salaries	6.00%
Prior to January 1, 2003 | Maximum
Defined Benefit Plan Disclosure [Line Items]
Service credits, percent of eligible salaries	12.00%
On or Subsequent to January 1, 2003
Defined Benefit Plan Disclosure [Line Items]
Service credits, percent of eligible salaries	6.00%