Retirement Benefit Plans (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020
Net Periodic Benefit Cost [Line Items]
Interest credit under cash balance plan			0.03
Employer matching contribution, percentage			5.00%
Employees' Pension Plan
Net Periodic Benefit Cost [Line Items]
Assumptions used calculating benefit obligation, interest rate to annuitize cash balance account					0.53%
Defined benefit plan, increase in benefit payable, percent	3.00%		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
Service Cost	$ 484,000	$ 416,000	$ 1,451,000	$ 1,247,000
Interest Cost	340,000	387,000	1,023,000	1,159,000
Expected Return on Plan Assets	(945,000)	(902,000)	(2,835,000)	(2,706,000)
Amortization of Prior Service (Credit) Cost	20,000	15,000	59,000	47,000
Amortization of Net Loss (Gain)	0	20,000	0	61,000
Net Periodic (Benefit) Cost	(101,000)	(64,000)	(302,000)	(192,000)
Plan Contributions During the Period	0	0	0	0
Estimated Future Contributions in the Current Fiscal Year	0		$ 0
Select Executive Retirement Plan
Net Periodic Benefit Cost [Line Items]
Assumptions used calculating benefit obligation, interest rate to annuitize cash balance account					2.31%
Defined benefit plan, amortization of service cost			12 years 6 months
Defined benefit plan, benefit obligation, period increase (decrease)			$ 122,797
Service Cost	146,000	102,000	437,000	306,000
Interest Cost	48,000	48,000	143,000	144,000
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	12,000	11,000	36,000	32,000
Amortization of Net Loss (Gain)	44,000	37,000	134,000	110,000
Net Periodic (Benefit) Cost	250,000	198,000	750,000	592,000
Plan Contributions During the Period	118,000	116,000	354,000	349,000
Estimated Future Contributions in the Current Fiscal Year	118,000		118,000
Post-Retirement Benefit Plans
Net Periodic Benefit Cost [Line Items]
Assumptions used calculating benefit obligation, interest rate to annuitize cash balance account					3.09%
Service Cost	27,000	30,000	82,000	92,000
Interest Cost	62,000	78,000	186,000	233,000
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	27,000	27,000	80,000	80,000
Amortization of Net Loss (Gain)	(22,000)	0	(66,000)	0
Net Periodic (Benefit) Cost	94,000	135,000	282,000	405,000
Plan Contributions During the Period	32,000	$ 54,000	87,000	$ 191,000
Estimated Future Contributions in the Current Fiscal Year	$ 32,000		$ 32,000
On or Subsequent to January 1, 2003
Net Periodic Benefit Cost [Line Items]
Service credits, percent of eligible salaries			6.00%
Minimum | Prior to January 1, 2003
Net Periodic Benefit Cost [Line Items]
Service credits, percent of eligible salaries			6.00%
Maximum | Prior to January 1, 2003
Net Periodic Benefit Cost [Line Items]
Service credits, percent of eligible salaries			12.00%