Derivative Instruments - Gains (Losses) on Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	$ 2,451	$ 12,307	$ (14,015)	$ (42,690)
Total current period settlements on derivatives	6,425	12,721	32,997	33,515
Non-trading
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	2,550	12,528	(14,019)	(42,741)
Total current period settlements on derivatives	6,489	12,764	33,153	33,677
Trading
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives, net	(99)	(221)	4	51
Total current period settlements on derivatives	$ (64)	$ (43)	(156)	(162)
Trading | Various acquisitions
Derivative Instruments, Gain (Loss) [Line Items]
Total current period settlements on derivatives			$ (300)	$ (900)