Retirement Plans (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 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
Plan 2020 [Member]
Retirement Plans [Abstract]
Expected pension contributions	958,000
Higman [Member] | Plan 2019 [Member]
Retirement Plans [Abstract]
Pension contributions	483,000
Higman [Member] | Plan 2020 [Member]
Retirement Plans [Abstract]
Pension contributions	479,000
Pension Plan [Member]
Components of net periodic benefit cost [Abstract]
Service cost	1,917,000	$ 1,768,000
Interest cost	3,890,000	4,207,000
Expected return on plan assets	(6,188,000)	(5,224,000)
Amortization of actuarial loss	232,000	678,000
Net periodic benefit cost	(149,000)	1,429,000
SERP [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0	0
Interest cost	10,000	13,000
Expected return on plan assets	0	0
Amortization of actuarial loss	9,000	7,000
Net periodic benefit cost	19,000	20,000
Other Postretirement Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	0	0
Interest cost	6,000	8,000
Amortization of actuarial loss	(131,000)	(135,000)
Net periodic benefit cost	$ (125,000)	$ (127,000)