Leases (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating and Finance Leases [Line Items]
Operating Lease, Right-of-Use Asset				$ 566,000
Lease, Cost [Abstract]
Operating Lease Cost	[1]	$ 393,000	$ 497,000
Amortization of Lease Assets		21,000	13,000
Interest on Lease Liabilities		4,000	2,000
Variable Lease Cost		91,000	138,000
Total Lease Cost		703,000	983,000
Lease Assets and Liabilities [Abstract]
Total		1,075,000	826,000
Current Liability		295,089	369,365
Total		1,148,000	857,000
Finance Lease Net of Accumulated Depreciation		40,673,147	36,938,066
Cash Flow Operating And Financing Activities [Abstract]
Operating Leases Non-Cash Leasing Activities		893,000	784,000
Operating And Finance Leases Future Minimum Payments [Abstract]
Operating And Finance Leases Not Yet Commenced		$ 100,000
Minimum Operating And Finance Leases Not Yet Commenced Lease Term		2 years
Maximum Operating And Finance Leases Not Yet Commenced Lease Term		9 years
Capital Leases Future Minimum Payments Due [Abstract]
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability		$ 174,000
Short-term Lease Cost		194,000	$ 333,000
Finance Leases
Lease Assets and Liabilities [Abstract]
Current Liability		31,000
Long-Term Liability		$ 181,000
Weighted Average Remaining Lease Term And Discount Rate [Abstract]
Finance Lease Weighted Average Remaining Lease Term (in years)		7 years 7 months 6 days	4 years 8 months 12 days
Finance Lease Weighted Average Discount Rate (%)		2.80%	3.00%
Cash Flow Operating And Financing Activities [Abstract]
Repayment of Finance Lease Liabilities		$ 19,000	$ 13,000
Operating And Finance Leases Future Minimum Payments [Abstract]
2021		36,000
2022		32,000
2023		28,000
2024		29,000
2025		27,000
2026 and Beyond		87,000
Total Lease Payments		239,000
Less: Discount to Present Value		27,000
Total Lease Liabilities		212,000
Capital Leases Future Minimum Payments Due [Abstract]
2019				15,000
2020				15,000
2021				15,000
2022				12,000
2023				8,000
2024 and Beyond				14,000
Total Leases Payments				79,000
Operating Leases [Member]
Lease Assets and Liabilities [Abstract]
Current Liability		295,000
Long-Term Liability		$ 641,000
Weighted Average Remaining Lease Term And Discount Rate [Abstract]
Operating Lease Weighted Average Remaining Lease Term (in years)		5 years 3 months 18 days	3 years 2 months 12 days
Operating Lease Weighted Average Discount Rate (%)		3.40%	3.50%
Operating And Finance Leases Future Minimum Payments [Abstract]
2021		$ 323,000
2022		210,000
2023		134,000
2024		96,000
2025		70,000
2026 and Beyond		206,000
Total Lease Payments		1,039,000
Less: Discount to Present Value		103,000
Total Lease Liabilities		936,000
Operating Leases Future Minimum Payments Due [Abstract]
2019				380,000
2020				213,000
2021				86,000
2022				39,000
2023				30,000
2024 and Beyond				62,000
Total Leases Payments				$ 810,000
Operating Leases [Member] | Operating Activities
Cash Flow Operating And Financing Activities [Abstract]
Repayment of Operating Lease Liabilities		223,000	$ 225,000
Operating Leases [Member] | Investing Activities
Cash Flow Operating And Financing Activities [Abstract]
Repayment of Operating Lease Liabilities		130,000	270,000
Property, Plant and Equipment
Lease Assets and Liabilities [Abstract]
Finance Lease Net of Accumulated Depreciation		81,000	60,000
Property, Plant and Equipment | Finance Leases
Operating and Finance Leases [Line Items]
Operating Lease, Right-of-Use Asset		869,000	773,000
Lease Assets and Liabilities [Abstract]
Right-of-Use Asset	[2]	206,000	53,000
Current Portion of Operating Lease Liabilities | Operating Leases [Member]
Lease Assets and Liabilities [Abstract]
Current Liability		295,000	369,000
Current Portion of Long-Term Debt | Finance Leases
Lease Assets and Liabilities [Abstract]
Current Liability		31,000	15,000
Other Liabilities | Operating Leases [Member]
Lease Assets and Liabilities [Abstract]
Long-Term Liability		641,000	430,000
Long-term Debt [Member] | Finance Leases
Lease Assets and Liabilities [Abstract]
Long-Term Liability		$ 181,000	$ 43,000

[1] Operating lease cost includes impairment expenses of $35 million in 2020.

[2] Finance lease assets are recorded net of accumulated amortization of $81 million and $60 million at December 31, 2020 and 2019, respectively.