Fair Value - Schedule of Fair Value of Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	$ 35,669	$ 43,222
Liability	97,348	82,203
Fair Value, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	12,061	10,283
Financial Liabilities Fair Value Disclosure	60,941	30,613
Counterparty and Cash Collateral Netting, Assets	(31,930)	(41,442)
Counterparty and Cash Collateral Netting, Liabilities	(36,407)	(51,590)
Fair Value, Recurring [Member] \| Fixed Income Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	2,498	2,232
Fair Value, Recurring [Member] \| Equity Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	5,824	6,271
Fair Value, Recurring [Member] \| Energy commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting, Assets	(31,923)	(40,452)
Derivative Asset	3,739	1,094
Counterparty and Cash Collateral Netting, Liabilities	(26,300)	(43,830)
Derivative Liability	724	1,314
Fair Value, Recurring [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting, Assets	(7)
Derivative Asset		97
Counterparty and Cash Collateral Netting, Liabilities	(7)
Derivative Liability	45
Fair Value, Recurring [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting, Assets		(27)
Counterparty and Cash Collateral Netting, Liabilities		(27)
Derivative Liability	3,674	2,976
Fair Value, Recurring [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and Cash Collateral Netting, Assets		(963)
Derivative Asset		589
Counterparty and Cash Collateral Netting, Liabilities	(10,100)	(7,733)
Derivative Liability	56,498	26,323
Fair Value, Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	8,322	8,503
Fair Value, Recurring [Member] \| Level 1 [Member] \| Fixed Income Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	2,498	2,232
Fair Value, Recurring [Member] \| Level 1 [Member] \| Equity Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	5,824	6,271
Fair Value, Recurring [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure	35,669	43,195
Financial Liabilities Fair Value Disclosure	93,674	79,200
Fair Value, Recurring [Member] \| Level 2 [Member] \| Energy commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	35,662	41,546
Liability	27,024	45,144
Fair Value, Recurring [Member] \| Level 2 [Member] \| Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	7	97
Liability	52
Fair Value, Recurring [Member] \| Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset		1,552
Liability	66,598	34,056
Fair Value, Recurring [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, Fair Value Disclosure		27
Financial Liabilities Fair Value Disclosure	3,674	3,003
Fair Value, Recurring [Member] \| Level 3 [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset		27
Liability	$ 3,674	$ 3,003

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, and obligation to return cash collateral under master netting arrangements.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, and right to receive cash collateral under master netting arrangements.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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