Derivative Instruments - Offsetting Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Total Derivative Liabilities
Offsetting Liabilities [Line Items]
Gross  Liabilities	$ (7,116)	$ (12,051)
Gross Amounts Offset	3,709	4,233
Net Liabilities	(3,407)	(7,818)
Cash Collateral Offset	13	86
Net Amount Presented	(3,394)	(7,732)
Total Current Derivative Liabilities
Offsetting Liabilities [Line Items]
Gross  Liabilities	(6,626)	(11,213)
Gross Amounts Offset	3,394	3,622
Net Liabilities	(3,232)	(7,591)
Cash Collateral Offset	13	86
Net Amount Presented	(3,219)	(7,505)
Non-trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross  Liabilities	(6,623)	(11,139)
Gross Amounts Offset	3,394	3,620
Net Liabilities	(3,229)	(7,519)
Cash Collateral Offset	13	86
Net Amount Presented	(3,216)	(7,433)
Trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross  Liabilities	(3)	(74)
Gross Amounts Offset	0	2
Net Liabilities	(3)	(72)
Cash Collateral Offset	0	0
Net Amount Presented	(3)	(72)
Total Non-current Derivative Assets
Offsetting Liabilities [Line Items]
Gross  Liabilities	(490)	(838)
Gross Amounts Offset	315	611
Net Liabilities	(175)	(227)
Cash Collateral Offset	0	0
Net Amount Presented	(175)	(227)
Non-trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross  Liabilities	(490)	(838)
Gross Amounts Offset	315	611
Net Liabilities	(175)	(227)
Cash Collateral Offset	0	0
Net Amount Presented	(175)	(227)
Trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross  Liabilities	0	0
Gross Amounts Offset	0	0
Net Liabilities	0	0
Cash Collateral Offset	0	0
Net Amount Presented	$ 0	$ 0