Derivative Instruments - Gains (Losses) on Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	$ 8,121	$ (35,456)	$ (16,466)	$ (54,997)
Total current period settlements on derivatives	9,964	12,769	26,572	20,794
Non-trading
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	7,964	(35,466)	(16,569)	(55,269)
Total current period settlements on derivatives	10,055	12,788	26,664	20,913
Trading
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	157	10	103	272
Total current period settlements on derivatives	$ (91)	$ (19)	(92)	(119)
Trading | Various Acquisitions
Derivative Instruments, Gain (Loss) [Line Items]
Total current period settlements on derivatives			$ (300)	$ (900)