Derivative Instruments - Gains (Losses) on Derivative Instruments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	$ (23,386,000)	$ (67,749,000)	$ (18,170,000)
Total current period settlements on derivatives	37,729,000	42,820,000	(10,587,000)
Non-trading
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	(23,439,000)	(67,955,000)	(19,571,000)
Total current period settlements on derivatives	37,921,000	42,944,000	(9,614,000)
Non-trading | Various Acquisitions
Derivative Instruments, Gain (Loss) [Line Items]
Total current period settlements on derivatives	0	100,000	(300,000)
Trading | Various Acquisitions
Derivative Instruments, Gain (Loss) [Line Items]
Total current period settlements on derivatives	300,000	(900,000)	0
Non-cash Flow Hedging | Non-trading
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	(23,439,000)	(67,955,000)	(19,571,000)
Total current period settlements on derivatives	37,921,000	42,944,000	(9,614,000)
Non-cash Flow Hedging | Trading
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	53,000	206,000	1,401,000
Total current period settlements on derivatives	$ (192,000)	$ (124,000)	$ (973,000)