Derivatives (Schedule of Fair Value of Derivative Assets and Liabilities) (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Embedded Derivative, Fair Value, Liability	$ (36,700,000)
Current Assets - Other | Commodity Derivatives | Not Designated As Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	503,000	$ 443,000
Derivative Asset, Fair Value, Gross Liability	(503,000)	(443,000)
Derivative Asset	0	0
Derivative Liability, Fair Value, Gross Liability	(1,167,000)	(1,772,000)
Derivative Liability, Fair Value, Gross Asset	1,167,000	1,772,000
Derivative Liability	0	0
Current Assets - Other | Commodity Derivatives | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	43,000	3,321,000
Derivative Asset, Fair Value, Gross Liability	(43,000)	(3,321,000)
Derivative Asset	0	0
Derivative Liability, Fair Value, Gross Liability	(2,643,000)	(9,506,000)
Derivative Liability, Fair Value, Gross Asset	2,459,000	7,589,000
Derivative Liability	(184,000)	(1,917,000)
Other long-term liabilities | Preferred Distribution Rate Reset Election
Derivatives, Fair Value [Line Items]
Embedded Derivative, Fair Value, Liability	$ (36,726,000)	$ 0