Pension Plans and Other Postretirement Benefits (Details-6) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Expected Cash Flows
Expected employer contributions, 2020	$ 0
Cash contributions to pension and other postretirement plans	5,714,000	$ 5,584,000	$ 11,304,000
Pension Benefits [Member]
Benefit Payments, Gross
Defined benefit plan expected future benefit payments, 2020	17,111,000
Defined benefit plan expected future benefit payments, 2021	17,859,000
Defined benefit plan expected future benefit payments, 2022	19,029,000
Defined benefit plan expected future benefit payments, 2023	19,942,000
Defined benefit plan expected future benefit payments, 2024	20,768,000
Defined benefit plan expected future benefit payments, 2025-2029	113,044,000
Postretirement Benefits [Member]
Benefit Payments, Gross
Defined benefit plan expected future benefit payments, 2020	4,580,000
Defined benefit plan expected future benefit payments, 2021	4,947,000
Defined benefit plan expected future benefit payments, 2022	5,161,000
Defined benefit plan expected future benefit payments, 2023	5,458,000
Defined benefit plan expected future benefit payments, 2024	5,676,000
Defined benefit plan expected future benefit payments, 2025-2029	28,054,000
Medicare Part D Subsidies
Expected Medicare Part D Subsidies, 2020	(233,000)
Expected Medicare Part D Subsidies, 2021	(255,000)
Expected Medicare Part D Subsidies, 2022	(283,000)
Expected Medicare Part D Subsidies, 2023	(307,000)
Expected Medicare Part D Subsidies, 2024	(330,000)
Expected Medicare Part D Subsidies, 2025-2029	(2,060,000)
Benefit Payments, Net
Defined benefit plan expected net future benefit payments, 2020	4,347,000
Defined benefit plan expected net future benefit payments, 2021	4,692,000
Defined benefit plan expected net future benefit payments, 2022	4,878,000
Defined benefit plan expected net future benefit payments, 2023	5,151,000
Defined benefit plan expected net future benefit payments, 2024	5,346,000
Defined benefit plan expected net future benefit payments, 2025-2029	$ 25,994,000