Retirement Plans (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Retirement Plans [Abstract]
Service period of participants not impacted by pension plan amendment				15 years
Age of plan participants not impacted by pension plan amendment				50 years
Service period of participants who are age fifty not impacted by pension plan amendment				10 years
Pension plan defined benefit plan cost increase limit percentage				4.00%
Plan 2019 [Member]
Retirement Plans [Abstract]
Expected pension contributions		$ 314,000		$ 314,000
Plan 2020 [Member]
Retirement Plans [Abstract]
Expected pension contributions		479,000		479,000
Higman [Member] | Plan 2019 [Member]
Retirement Plans [Abstract]
Pension contributions				483,000
Higman [Member] | Plan 2020 [Member]
Retirement Plans [Abstract]
Pension contributions				479,000
Higman [Member] | Plan 2020 [Member] | Subsequent Events [Member]
Retirement Plans [Abstract]
Pension contributions	$ 479,000
Pension Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost		1,919,000	$ 1,914,000	3,836,000	$ 3,682,000
Interest cost		3,949,000	4,040,000	7,839,000	8,247,000
Expected return on plan assets		(5,735,000)	(5,254,000)	(11,923,000)	(10,478,000)
Amortization of actuarial loss		425,000	41,000	657,000	719,000
Net periodic benefit cost		558,000	741,000	409,000	2,170,000
SERP [Member]
Components of net periodic benefit cost [Abstract]
Service cost		0	0	0	0
Interest cost		10,000	13,000	20,000	26,000
Expected return on plan assets		0	0	0	0
Amortization of actuarial loss		9,000	7,000	18,000	14,000
Net periodic benefit cost		19,000	20,000	38,000	40,000
Other Postretirement Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost		0	0	0	0
Interest cost		5,000	8,000	11,000	16,000
Amortization of actuarial loss		(130,000)	(135,000)	(261,000)	(270,000)
Net periodic benefit cost		$ (125,000)	$ (127,000)	$ (250,000)	$ (254,000)