Derivative Instruments - Offsetting Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Total Derivative Liabilities
Offsetting Liabilities [Line Items]
Gross  Liabilities	$ (23,988)	$ (36,579)
Gross Amounts Offset	11,713	14,475
Net Liabilities	(12,275)	(22,104)
Cash Collateral Offset	585	1,666
Net Amount Presented	(11,690)	(20,438)
Total Current Derivative Liabilities
Offsetting Liabilities [Line Items]
Gross  Liabilities	(23,500)	(34,628)
Gross Amounts Offset	11,633	13,053
Net Liabilities	(11,867)	(21,575)
Cash Collateral Offset	585	1,632
Net Amount Presented	(11,282)	(19,943)
Non-trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross  Liabilities	(23,334)	(34,434)
Gross Amounts Offset	11,467	12,859
Net Liabilities	(11,867)	(21,575)
Cash Collateral Offset	585	1,632
Net Amount Presented	(11,282)	(19,943)
Trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross  Liabilities	(166)	(194)
Gross Amounts Offset	166	194
Net Liabilities	0	0
Cash Collateral Offset	0	0
Net Amount Presented	0	0
Total Non-current Derivative Assets
Offsetting Liabilities [Line Items]
Gross  Liabilities	(488)	(1,951)
Gross Amounts Offset	80	1,422
Net Liabilities	(408)	(529)
Cash Collateral Offset	0	34
Net Amount Presented	(408)	(495)
Non-trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross  Liabilities	(488)	(1,951)
Gross Amounts Offset	80	1,422
Net Liabilities	(408)	(529)
Cash Collateral Offset	0	34
Net Amount Presented	(408)	(495)
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