Derivatives (Fair Value of Derivative Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Liability Derivatives:
Preferred Distribution Rate Reset Election	$ (52,400)
Embedded Derivative Financial Instruments | Other Noncurrent Liabilities [Member]
Liability Derivatives:
Preferred Distribution Rate Reset Election	(52,372)	$ (51,515)
Not Designated As Hedging Instrument | Commodity Derivatives | Current Assets - Other
Asset Derivatives:
Gross amount of recognized assets	732	207
Gross amount offset in the Consolidated Balance Sheets	(732)	(207)
Net amount of assets presented in the Consolidated Balance Sheets	0	0
Liability Derivatives:
Gross amount of recognized liabilities	(2,114)	(2,079)
Gross amount offset in the Consolidated Balance Sheets	2,114	1,064
Net amount of liabilities presented in the Consolidated Balance Sheets	0	(1,015)
Not Designated As Hedging Instrument | Swap | Current Assets - Other
Asset Derivatives:
Gross amount of recognized assets	616	1,382
Not Designated As Hedging Instrument | Swap | Current Liabilities - Accrued Liabilities
Liability Derivatives:
Gross amount of recognized liabilities	0	0
Designated as Hedging Instrument | Commodity Derivatives | Current Assets - Other
Asset Derivatives:
Gross amount of recognized assets	1,022	4
Gross amount offset in the Consolidated Balance Sheets	(1,022)	(4)
Net amount of assets presented in the Consolidated Balance Sheets	0	0
Liability Derivatives:
Gross amount of recognized liabilities	(3,345)	(50)
Gross amount offset in the Consolidated Balance Sheets	3,073	50
Net amount of liabilities presented in the Consolidated Balance Sheets	$ (272)	$ 0