Derivatives (Fair Value of Derivative Assets and Liabilities) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Liability Derivatives:
Preferred Distribution Rate Reset Election		$ (45,200)
Current Assets-Other [Member]
Asset Derivatives:
Total asset derivatives		0	$ 0
Embedded Derivative Financial Instruments [Member] | Other Noncurrent Liabilities [Member]
Liability Derivatives:
Preferred Distribution Rate Reset Election	[1]	(45,209)	0
Not Designated As Hedging Instrument [Member] | Commodity Derivatives [Member] | Current Assets-Other [Member]
Asset Derivatives:
Gross amount of recognized assets		505	443
Gross amount offset in the Consolidated Balance Sheets		(505)	(443)
Net amount of assets presented in the Consolidated Balance Sheets		0	0
Liability Derivatives:
Gross amount of recognized liabilities	[2]	(1,203)	(1,772)
Gross amount offset in the Consolidated Balance Sheets	[2]	1,203	1,772
Net amount of liabilities presented in the Consolidated Balance Sheets		0	0
Designated as Hedging Instrument [Member] | Commodity Derivatives [Member] | Current Assets-Other [Member]
Asset Derivatives:
Gross amount of recognized assets		54	3,321
Gross amount offset in the Consolidated Balance Sheets		(54)	(3,321)
Net amount of assets presented in the Consolidated Balance Sheets		0	0
Liability Derivatives:
Gross amount of recognized liabilities	[2]	(863)	(9,506)
Gross amount offset in the Consolidated Balance Sheets	[2]	338	7,589
Net amount of liabilities presented in the Consolidated Balance Sheets		$ (525)	$ (1,917)

[1] Refer to Note 11 and Note 19 for additional discussion surrounding the Preferred Distribution Rate Reset Election derivative.

[2] These derivative liabilities have been funded with margin deposits recorded in our Consolidated Balance Sheets under Current Assets - Other.