Derivatives (Schedule of Fair Value of Derivative Assets and Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Embedded Derivative, Fair Value, Liability	$ (42,200)
Preferred Distribution Rate Reset Election \| Other long-term liabilities
Derivatives, Fair Value [Line Items]
Embedded Derivative, Fair Value, Liability	(42,183)	$ (40,840)
Not qualifying or not designated as hedges under accounting rules \| Commodity Derivatives \| Current Assets - Other
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,685	3,431
Derivative Asset, Fair Value, Gross Liability	(1,685)	(1,361)
Derivative Asset	0	2,070
Derivative Liability, Fair Value, Gross Liability	(2,871)	(1,361)
Derivative Liability, Fair Value, Gross Asset	2,871	1,361
Derivative Liability	0	0
Not qualifying or not designated as hedges under accounting rules \| Swap \| Current Assets - Other
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	361	1,274
Not qualifying or not designated as hedges under accounting rules \| Swap \| Current Liabilities - Accrued Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(186)	(125)
Designated as hedges under accounting rules \| Commodity Derivatives \| Current Assets - Other
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	161	469
Derivative Asset, Fair Value, Gross Liability	(161)	(44)
Derivative Asset	0	425
Derivative Liability, Fair Value, Gross Liability	(7)	(44)
Derivative Liability, Fair Value, Gross Asset	7	44
Derivative Liability	$ 0	$ 0

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.

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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, after the 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 not subject to a master netting arrangement and not elected to be offset.

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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 as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as a liability.

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