Retirement Benefit Plans (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	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	$ 507,000	$ 401,000	$ 967,000	$ 831,000
Interest Cost	343,000	355,000	683,000	772,000
Expected Return on Plan Assets	(940,000)	(900,000)	(1,890,000)	(1,804,000)
Amortization of Prior Service (Credit) Cost	19,000	16,000	39,000	32,000
Amortization of Net Loss (Gain)	0	40,000	0	41,000
Net Periodic (Benefit) Cost	(71,000)	(88,000)	(201,000)	(128,000)
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	173,000	101,000	291,000	204,000
Interest Cost	50,000	42,000	95,000	96,000
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	12,000	10,000	24,000	21,000
Amortization of Net Loss (Gain)	52,000	40,000	90,000	73,000
Net Periodic (Benefit) Cost	287,000	193,000	500,000	394,000
Plan Contributions During the Period	118,000	116,000	236,000	233,000
Estimated Future Contributions in the Current Fiscal Year	236,000		236,000
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	24,000	29,000	55,000	62,000
Interest Cost	57,000	77,000	124,000	155,000
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	26,000	26,000	53,000	53,000
Amortization of Net Loss (Gain)	(52,000)	(2,000)	(44,000)	0
Net Periodic (Benefit) Cost	55,000	130,000	188,000	270,000
Plan Contributions During the Period	27,000	$ 59,000	55,000	$ 137,000
Estimated Future Contributions in the Current Fiscal Year	$ 54,000		$ 54,000
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%