Derivative Instruments - Offsetting Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Total Derivative Liabilities
Offsetting Liabilities [Line Items]
Gross Liabilities	$ (42,574)	$ (36,579)
Gross Amounts Offset	12,731	14,475
Net Liabilities	(29,843)	(22,104)
Cash Collateral Offset	1,561	1,666
Net Amount Presented	(28,282)	(20,438)
Total Current Derivative Liabilities
Offsetting Liabilities [Line Items]
Gross Liabilities	(39,940)	(34,628)
Gross Amounts Offset	11,935	13,053
Net Liabilities	(28,005)	(21,575)
Cash Collateral Offset	1,555	1,632
Net Amount Presented	(26,450)	(19,943)
Non-trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross Liabilities	(39,814)	(34,434)
Gross Amounts Offset	11,809	12,859
Net Liabilities	(28,005)	(21,575)
Cash Collateral Offset	1,555	1,632
Net Amount Presented	(26,450)	(19,943)
Trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross Liabilities	(126)	(194)
Gross Amounts Offset	126	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	(2,634)	(1,951)
Gross Amounts Offset	796	1,422
Net Liabilities	(1,838)	(529)
Cash Collateral Offset	6	34
Net Amount Presented	(1,832)	(495)
Non-trading commodity derivatives
Offsetting Liabilities [Line Items]
Gross Liabilities	(2,634)	(1,951)
Gross Amounts Offset	796	1,422
Net Liabilities	(1,838)	(529)
Cash Collateral Offset	6	34
Net Amount Presented	(1,832)	(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