Derivative Instruments - Gains (Losses) on Derivative Instruments (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	$ (24,587,000)	$ (19,541,000)
Total current period settlements on derivatives	16,608,000	8,025,000
Non-trading
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	(24,533,000)	(19,803,000)
Total current period settlements on derivatives	16,609,000	8,125,000
Trading
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	(54,000)	262,000
Total current period settlements on derivatives	(1,000)	(100,000)
Trading | Various Acquisitions
Derivative Instruments, Gain (Loss) [Line Items]
Total current period settlements on derivatives	$ (300,000)	$ (900,000.0)