Derivatives and Risk Management - Schedules of Fair Values and Locations of Derivative Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Gross Asset	$ 24,702	$ 43,222
Gross Liability	(83,280)	(82,203)
Collateral Netting	8,666	10,148
Net Asset (Liability) on Balance Sheet	(49,912)	(28,833)
Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Collateral Netting	616	3,378
Other Current Assets [Member] \| Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	30	97
Net Asset (Liability) on Balance Sheet	30	97
Other Current Assets [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset		589
Net Asset (Liability) on Balance Sheet		589
Other Current Assets [Member] \| Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	9,203	416
Gross Liability	(8,306)	(245)
Net Asset (Liability) on Balance Sheet	897	171
Other Current Liabilities [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset		238
Gross Liability	(19,575)	(9,379)
Collateral Netting	8,050	1,316
Net Asset (Liability) on Balance Sheet	(11,525)	(7,825)
Other Current Liabilities [Member] \| Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	11,037	34,760
Gross Liability	(14,007)	(41,241)
Collateral Netting	487	3,378
Net Asset (Liability) on Balance Sheet	(2,483)	(3,103)
Other Noncurrent Liabilities [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	952	725
Gross Liability	(32,190)	(24,677)
Collateral Netting		5,454
Net Asset (Liability) on Balance Sheet	(31,238)	(18,498)
Other Noncurrent Liabilities [Member] \| Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	1,725	28
Gross Liability	(8,043)	(1,215)
Collateral Netting	129
Net Asset (Liability) on Balance Sheet	(6,189)	(1,187)
Other Property And Investments Net And Other Non-current Assets [Member] \| Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	1,755	6,369
Gross Liability	(1,159)	(5,446)
Net Asset (Liability) on Balance Sheet	$ 596	$ 923

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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